P0171 trouble code? (Solved)

The OBDII trouble code P0171 – System Too Lean (Bank 1) means that the engine air-fuel mixture is too lean, or there is too much air and too little fuel. Driving a car with the code P0171 can cause more damage to the engine over time, as when the engine runs lean, the combustion temperature is higher.

How do you fix code P0171?

What repairs can fix the P0171 code?

  1. Replacing the fuel pump.
  2. Replacing the fuel filter.
  3. Replacing the fuel pressure regulator.
  4. Replacing the powertrain control module.
  5. Replacing one or more injectors.
  6. Replacing one or more oxygen sensors.
  7. Replacing the mass air flow sensor.
  8. Repairing a vacuum leak.

What would cause a P0171 code?

This can be caused by something like a disconnected hose or vacuum leak, which means there’s more air than usual, or because your fuel system is weak. P0171 is a common trouble code in many vehicles. If there is too much air, the ECM or PCM overcompensates with larger fuel injections, which triggers the P0171 code.

Can a bad O2 sensor cause P0171?

A P0171 or P0174 lean code with an O2 sensor reading lean all the time mean — well, several things. The real problem may not be a bad O2 sensor, but possibly be an engine vacuum leak, low fuel pressure or dirty fuel injectors that are causing the engine run lean.

Can code P0171 cause misfire?

What are the symptoms for a P0171 code? Generally, a lean code will cause the engine to run poorly, which the driver will notice as a high idle, a misfire, a lack of power, or even engine stalling, and this may happen before the check engine light has turned on.

How do you fix lean air/fuel mixture?

Vacuum leak: Vacuum leaks can cause a lean fuel mixture. Inspecting and replacing damaged vacuum lines with good hoses and clamps can solve a lean problem. Clogged fuel filter: clogged fuel filters will limit the amount of fuel requires by the engine.

Can a dirty air filter cause a lean code?

If the filter is clogged or excessively dirty, this is enough to impede or restrict the air flow, hence resulting in a lean running condition. Besides a dirty air filter, the P0171 code can also be blamed on a dirty or faulty MAF sensor and a clogged fuel filter.

Is it OK to drive with P0171 code?

It is okay to drive a vehicle with P0171 for a short period of time, but driving with this code for an extended period of time can overheat the engine and cause internal engine damage.

Can a bad gas cap cause a P0171 code?

It doesn’t set a code that is false. A lean code from a vacuum leak, mass air flow failure, pcv valve bad or low fuel pressure is 171.

Can bad spark plugs cause P0171?

Not likely. A P0171 ( too lean, Bank 1 ) code is most often caused by a vacuum leak downstream from the MAF sensor or a malfunctioning MAF sensor. Bad spark plugs could actually cause the opposite code ( too rich, bank 1).

Can a bad PCV valve cause P0171?

The most common causes of the P0171 code are vacuum or intake leaks, low fuel pressure, faulty PCV valve, or a faulty MAF sensor. Other things can also cause the P0171 code.

What causes P0171 and P0174 codes Chevy?

A P0171 or P0174 trouble code can happen because of a vacuum leak or faulty sensor. Vacuum leak faults usually—not always—manifest more readily at lower speeds; as a rough idle, for example. A capable scan tool can check fuel trim values at idle and at higher engine speeds and detect when the lean condition occurs.

What happens if fuel mixture too lean?

Too lean a mixture will result in popping or a misfire; too rich a mix produces sooty smoke and a flame that won’t cut. For proper torch operation, you need a proper mixture. When you think of lean as meaning not enough fuel for the amount of air, you start with the concept that the amount of air is correct.

What does Bank 2 too lean mean?

Error code P0174 is described as System Too Lean (Bank 2). This means there is incorrect ratio of air and fuel on the car’s engine system, specifically on Bank 2 of the Cylinder. “Too Lean” means there is too much oxygen in the exhaust.

How much does it cost to fix a system too lean Bank 1?

P0171: System Too Lean Bank 1. Most auto repair shops charge between $75 and $150 per hour. P0171 – System to Lean (Bank 1) P0174 – System to Lean (Bank 2) Lack of fuel or too much air – unmetered air after the mass air flow sensor!

P0171 Diagnostic Trouble Code – What You Need to Know

Because the engine is running low on bank 1, the air to fuel ratio is heavily skewed in favor of the air.

What P0171 really means

The computer can make corrections over time as the engine ages, components fail or measurement sensors become defective. The computer may do this by increasing the amount of time the fuel injectors are turned on in order to richen the mixture. This code can also be used in conjunction with a P0174, which will indicate that bank 2 is lean. To achieve optimal combustion efficiency, the ideal stoichiometric ratio is 14.7 parts air to 1 part fuel. This provides for an excellent combination of fuel economy, performance, and fewer emissions during combustion.

What are the symptoms for a P0171 code?

It is common for lean codes to cause the engine to run badly, which the driver would notice as a high idle, a misfire, a loss of power, or even engine stalling. This can occur even before the check engine light illuminates. Furthermore, these symptoms will be more obvious at slower speeds and lower RPMs than at higher speeds and RPMs. The engine is better able to deal with lean conditions at higher speeds since the demand for air is larger.

What is the severity of a P0171 code?

Critical. A diagnostic check should be performed as soon as possible to determine the specific nature of the problem.

What repairs are required for a P0171 code?

There is a broad list of reasons why the engine runs lean, and a qualified technician will require time to figure out what is causing the issue. The problem, in contrast to rich difficulties, can occur on either side of the mixture – either too much air or not enough fuel. To be sure, there are some straightforward solutions – a broken vacuum line will allow air into the vehicle that the computer cannot account for, and a blocked fuel filter would reduce the amount of fuel that can be delivered.

What is the cost to resolve a P0171 code?

  • It is estimated that the diagnostic cost will be $100
  • That the part(s) and labor costs will be $50–$800 (depending on the diagnosis)
  • And that the overall cost will be $150–900.

This code will necessitate a diagnostic check, which will cost around $100 depending on how long it takes to identify the problem. In light of the fact that there is a laundry list of reasons why the engine runs thin, the average cost of each repair will vary significantly. Perhaps one of the easy fixes listed above will turn out to be a fortuitous break. A damaged vacuum hose sucking in air can cost as little as $50, while a blocked fuel filter might cost as much as $100. An oxygen sensor or a mass air flow sensor, on the other hand, can result in a cost of $400 to $500 dollars.

If your car is displaying this code, you should arrange a diagnostic check with a professional as soon as possible.

It’s not an issue.

Written by an ASE Master Technician, this service article provides information on Obtain price quotes from neighboring businesses.

P0171 – Meaning, Causes, Symptoms, & Fixes

Bank 1 either contains an excessive amount of air or an insufficient amount of fuel.

What Does P0171 Mean?

Combustion engines operate most efficiently when the air-to-fuel mixture ratio is maintained at 14.7 parts air to one part fuel. There is a lean state present when there is more than 14.7 parts air to 1 part fuel in the air-fuel combination, and the code P0171 is activated. In addition to vacuum leaks, which bring more air into the air-fuel mixture, a weak fuel system, which does not inject enough fuel into the air-fuel combination, can result in a lean situation as a result of a weak fuel system.

When the magnitude of these modifications exceeds a certain threshold, code P0171 is triggered.

What Are The Symptoms Of P0171?

  • Check Engine The engine is not producing enough power
  • The engine is making a rough idle
  • The engine is coughing
  • The engine is misfiring.

What Is The Cause Of P0171?

  • Clean or malfunctioning mass airflow sensor
  • PCV hoses, vacuum hoses, and the intake manifold gasket all have vacuum leaks. Fuel pump that is not working properly
  • Fuel injectors that are clogged or filthy
  • Fuel filter that has become clogged
  • Leak in the exhaust system
  • Faulty oxygen sensor
  • Faulty air-fuel ratio sensor
  • Faulty oxygen sensor

How Serious Is Code P0171? – Moderate

Driving a vehicle with the P0171 code for a short amount of time is OK; however, driving a vehicle with this code for a longer period of time might cause the engine to overheat and cause internal engine damage.

Code P0171 Common Diagnosis Mistakes

Driving a car with the P0171 code for a short amount of time is OK; however, driving a vehicle with this code for a longer period of time might cause the engine to overheat and cause internal engine damage to the vehicle.

Tools Needed To Diagnosis P0171

  • You Might Require the Following Tools: (FIXD’s top-recommended Amazon selections are as follows:
  • In addition to FIXD ($59.99), Mass Air Flow Cleaner ($11.31), Fuel Pressure Testing Gauge ($25.99), and Hayne’s Repair Manual ($19-$25), there are several more items to consider.

How To Diagnosis Code P0171

Diagnose and repair are difficult — 3 out of 5 on the difficulty scale.

  1. P0171 is the only code that should be present, therefore scan your car using FIXD to confirm. If there are any additional codes present, they must be dealt with first. Check for leaks in any vacuum lines and hoses, and double-check that they are all securely linked together. While driving, you will hear a hissing sound that indicates the presence of a leak. However, it may be difficult to detect while the engine is running. Look out this comprehensive guide to discovering and correcting vacuum leaks if you believe you have one but are having difficulty locating it
  2. After reconnecting any disconnected vacuum lines and replacing any broken vacuum lines that are leaking, use FIXD to delete the check engine light code P0171 from the vehicle’s computer. Once again, if the check engine light (code P0171) illuminates, check for leaks in the remaining vacuum lines before continuing with the rest of the diagnostic procedure. Remove the mass airflow sensor and clean it with a mass airflow cleaner or a contact cleaner before reinstalling it. Using FIXD, reinstall the mass airflow sensor and reset the check engine light on the vehicle. The diagnostic process should be repeated if the check engine light comes back on and displays code P0171. If you have determined that there are no vacuum leaks, that your mass airflow sensor is clean, and that your fuel system is operating correctly, check the exhaust for leaks before checking the Air Fuel Ratio Sensors or the Oxygen Sensors
  3. If you discover any leaks, get them fixed. You may want to investigate changing your A/F sensor or O2 sensors at this stage if the code still persists beyond this point.

Estimated Cost of Repair

If you receive error code P0171, one or more of the fixes listed below may be required to resolve the underlying problem. The estimated cost of repair for each feasible repair includes the cost of the essential components as well as the cost of the labor required to complete the repair, if any.

  • Clean the MAF for $100
  • Replace the MAF for $300
  • Fuel Pump $1300-$1700
  • Fuel pressure regulator $200-$400
  • Exhaust repair $100-$200 (if welded to repair)
  • Air fuel sensor or oxygen sensor $200-$300
  • Exhaust repair $100-$200 (if welded to repair).

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OBD-II DTC: P0171 System Too Lean (Bank 1)

System Is Far Too Sparse (Bank 1)

What does that mean?

This diagnostic problem code (DTC) is a general powertrain code that may be seen on many vehicles. Although particular repair processes may alter significantly depending on the model, it is called general since it applies to all makes and models of automobiles manufactured after 1996. As a result, this engine code article is applicable to Toyota, Chevrolet, Ford, Nissan, Honda, GMC, Dodge, and other manufacturers. To put it another way, this says that an oxygen sensor in bank 1 has identified a low oxygen level (too much oxygen in the exhaust).

P0171 is one of the more often encountered error codes.

As a result of the sensor’s output, the vehicle’s powertrain/engine control module (PCM/ECM) can determine the air-to-fuel ratio exiting the cylinders, and it can alter the engine’s operation to maintain that ideal ratio of 14.7:1.

For a better understanding of the engine’s operation, you should also read our article on short and long term fuel trims. Note: This DTC is quite similar to P0174, and your car may actually display both codes at the same time if you have both codes enabled.


More than likely, you will not notice any drivability issues, yet you may have symptoms such as:

  • An inability to generate sufficient power
  • Detonation (spark knock)
  • A harsh idle
  • Hesitancy or surge when accelerating


One or more of the following may have occurred when a codeP0171 was generated:

  • The MAF (Mass Air Flow) Sensor is clogged or defective, and the engine will not start. The use of “oiled” air filters, especially if the filter is over-oiled, may cause the MAF to get clogged and unclean. The MAF sensors on some cars also have a problem in that they leach out the silicone potting material that was intended to cover the electronics. It is possible that there is a vacuum leak downstream of the MAF sensor. Possibility of a fractured vacuum or PCV line or connector
  • PCV valve that is faulty or has become jammed open
  • The oxygen sensor in bank 1 (sensor 1) has failed or is defective. Fuel injector that has become stuck or blocked, or one that has failed. A low level of fuel pressure (perhaps due to a clogged or filthy fuel filter! )
  • Between the engine and the first oxygen sensor, there is an exhaust leak.

Possible Solutions

Cleaning the MAF sensor and locating and repairing vacuum leaks are two common solutions to this problem. If you’re on a limited budget, this is a good place to start, but it’s not always the best solution. As a result, some viable solutions are as follows:

  • Make sure the MAF sensor is clean. If you need assistance, consult your service manual to determine where it is located. Remove it and spray it with electronics cleaning or brake cleaner, I’ve found, to be the most effective method. Make cautious not to damage the MAF sensor during the process, and that it is completely dry before replacing it. Replace or repair any damaged suction or PCV hoses that are discovered. Evaluate and repair any damage to any hoses or connectors in the air intake system. Make a visual inspection and/or leak test of the intake manifold gaskets
  • Check for a clogged fuel filter as well as for sufficient fuel pressure. Ideally, you’ll want to use an advanced scan tool to keep track of both short- and long-term fuel trims. If you have access to a smoke tester, you may wish to use it.
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Related DTC Discussions

  • P0327, P0171, and P0174 are the codes for the 1999 Chevrolet Silverado. Okay, folks, I’m back with the same issue. Please help. Here’s what I’ve been up to since August of 2008. Replaced MAF sensor, air filter and knock sensor
  • Fuel pump
  • Coil
  • Tps
  • Fuel filter
  • Distributor cap and rotor
  • And distributor cap and rotor with new parts. But, guess what? I’m still getting the same numbers in this order: P0327, P0171, and P0174, which is the same as before. I’m travelling from P0171 to P0172 in a 2003 Trailblazer 4×4 with a 6 cylinder engine. P0171 is displayed on the scanner, but there is no service light illuminated
  • Nonetheless, after approximately 30 miles, P0172 becomes active and illuminates the service engine light. It appears to be operating normally, but no one has been able to figure out the 172 code for wealthy bank 1. Trim codes were re-calibrated, and the engine computer was updated. Codes for the 1997 Ford F-150 were seen three times. P0171P0174 I have a Ford F-150 with a 4.2L V6 engine and around 141,000 miles on it. I changed the spark plugs and wires since it had been over a year and a half since they had been replaced and the vehicle was starting to run rough. After replacing the spark plugs, the engine began to run more rough. It’s attempting to stall at red lights unless I do anything about it
  • P0171 – 2010 GMC Terrain SLE Greetings, and good morning. It’s been many years since I purchased my 2010 GMC Terrain, and the engine was changed approximately two years ago due to an oil consumption issue. As a result, I now have a new/refurbished engine in my Terrain. I’ve been getting the P0171 code lately, and suffice it to say, I’ve been informed it may be anything and anything
  • P0171 on a 1998 Dodge Stratus, to be precise. Anybody have experience with this code after changing the MAP sensor, EGR valve, O2 sensors, Fuel pump/regulator, plugs, and wires in their vehicle? At idle, the spark is erratic, and the plugs (mostly 1,4) begin to fill up. Despite traveling at highway rates, the code did not arrive for another 150 miles. When I pulled through a drive-thru, the id read 2002 F-150 with p0174 and p0171 on the dash. My truck was flashing codes 174 (lean mixture in bank 2) and 307 the day before yesterday (misfire cylinder 7). So, because they all had 175k miles on them, I changed the spark plugs in all eight of them. Yesterday evening, the truck performed like a brand new vehicle. This morning it began to go missing again, and the check engine light illuminated once again
  • P0171P0174 codes for a 2003 Ford Taurus SES (no real symptoms) 2003 Ford Taurus Session with 47,000 miles on it History: I just had my oil changed, tires rotated, and air filter replaced. A week later, I discovered water on the passenger floor of my vehicle (after it was raining a lot in octobermy car had been sitting outside). It was the first time I saw it, and it was verified by others
  • Montana p0302 and p0171 in 2000. This essay is about a 2000 Pontiac Montana with a 3.4L V6 automatic transmission and 158,000 kilometers. I recently cleaned the intake system since my oil analysis revealed that the combustion chambers were unclean. I ran some cleaner through the intake system and then out the exhaust system (smoke screen behind the van). Following that, a p0302 was established. Finding the ignition on a 2001 V6 3.8 Camaro
  • P0171 and P0174 are the codes. I’ve changed the fuel injectors, fuel filter, spark plugs, air filter, and fuel pump on my car. I’ve also replaced the fuel pump. Now that we’ve gotten that out of the way, let me tell you about my dilemma. I first started getting a P0171, and the code would clear itself after a few minutes, but I continued to get it around twice a month. Afterwards, I began to receive more of these codes: P0171 and P0174, and finally P0300 for a 2000 Isuzu Rodeo. I had P0171 and P0174 on my computer two days ago, and the truck’s idle was off, with hesitation on acceleration response. I cleaned the MAF with contact cleaner after inspecting the ducting leading to the air filter. Cleared the codes and drove the vehicle for another day
  • The codes did not reappear, but the engine was still not running properly. Today

Need more help with a p0171 code?

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How to Fix P0171 Code – Symptoms, Diagnosis, and Repair Tips

Your morning is going swimmingly, and you’re on your way to work on time—that is, until you try to start your car and discover that your Check Engine light is up and the engine is running rough. You pull out your trustyOBD IIscan tool or code reader and discover that you have a P0171 error code.

What does code P0171 mean?

In this case, the code indicates that there is either too much oxygen or too little fuel in the exhaust, referred to as a “lean” situation, or a lean or “low fuel trim” code in this case. This can be caused by anything as simple as a detached hose or vacuum leak, which results in the presence of more air than normal, or as complex as a faulty fuel system. P0171 is a problem code that may be found in many different cars. Bank 1 is the side of the engine where each of your car’s cylinders is located, while bank 2 is the same as “bank 1.” Bank 1 is where cylinder number 1 is situated, and it is here that you will find the source of the error code.

  1. This mixture ratio is quite exact, and if it is inaccurate by even a little amount, you might suffer the symptoms associated with a P0171 engine code if the mixture ratio is incorrect.
  2. What is the proper ratio to use?
  3. The engine or powertrain control module (ECM or PCM) in your automobile is responsible for monitoring the air-fuel mixture and adjusting the quantity of fuel used in accordance with the amount of air present.
  4. When there is too much air in the system, the ECM or PCM overcompensates by increasing the amount of fuel injected, resulting in the P0171 code being displayed.

How serious is a P0171 code?: Is it OK to drive with P0171?

In this case, the code indicates that there is either too much oxygen or too little fuel in the exhaust, referred to as a “lean” situation, or a lean or “low fuel trim” code, in the engine’s exhaust system. Depending on the cause, it might be due to a detached hose or a vacuum leak, which would result in more air than normal, or it could be due to a weak fuel system. A typical fault code in many automobiles is P0171. What does this mean? Bank 1 is the side of the engine where each of your car’s cylinders is located, while bank 2 is the same as “bank 3.” You’ll discover the source of the code in bank 1 since it’s where cylinder number 1 is situated.

This mixture ratio is quite exact, and if it is incorrect by even a tiny amount, you might suffer the symptoms associated with a P0171 engine code if the mixture ratio is not correct.

I’m not sure what the proper ratio is.

The engine or powertrain control module (ECM or PCM) in your automobile measures the air-fuel mixture with the assistance of oxygen sensors and regulates the quantity of fuel used in accordance with the amount of air present.

When there is an excessive amount of air in the system, the ECM or PCM overcompensates by increasing the amount of fuel injected, resulting in the P0171 code being displayed.

What are common P0171 code symptoms?

Symptoms of code P0171 include the following:

  • The Check Engine light is illuminated
  • Troublestartingyourengine
  • Engine that is difficult to start
  • Having difficulty idling or accelerating
  • Misfiring, halting, or losing power are all possible outcomes.

Code P0171 causes and how to diagnose them

P0171 problems can be caused by a variety of difficulties ranging from simple to complicated, and they can differ from vehicle to vehicle. Watch this video for professional mechanic assistance in identifying the reasons of the P0171 error code, and continue reading for additional information:

Video: Check Engine Light? System Too Lean – Code P0171, P0174

  • Discover and connect the airbox snorkel that links to the engine on your vehicle. Take a hold of it and shake it to see if there is anything loose. Alternatively, if the snorkel looks to be in good condition, you might inspect this region for any further disconnections. Under the engine cover, you’ll find: Look for anything that seems to be disconnected, as well as any open ports that appear to be missing a hose or a hose connector. Additionally, look for any restricted ports. Whistling noises when your automobile is running include the following: Begin by starting your engine and listening closely for any whistling or rushing air sounds beneath the hood, making sure to keep your hands away from any moving components. Do you hear anything? Start by inspecting the place where the noises are coming from for signs of a leak, an open port, or a loose hose. When trying to diagnose code P0171, you should be diligent because the code’s cause might be something as little as a pinhole in one of the lines.

Dirty, faulty, or damaged mass air flow sensor or air filter

  • The airbox snorkel is located near the engine and should be identified. Shake it up a little so you can check for any loose parts. Assuming the snorkel looks to be in good condition, you should inspect the surrounding region for any further disconnections. A look behind the engine cover reveals the following information: Keep an eye out for anything that appears to be detached, as well as any open ports that appear to be missing a hose or a connector. Examine your network to see if any ports have been restricted. The following are examples of whistling noises that can be heard while driving: Start your engine and pay close attention for any whistling or rushing air sounds beneath the hood while keeping your hands away from any moving components. Any noises in the background? If you’re hearing noises, start looking for a leak, open port, or a loose hose in the location where the noises are coming from. When trying to diagnose code P0171, you should be meticulous because the code’s cause might be something as simple as a pinhole in one of the lines.

Diagnosis difficulty: Advanced

  • Cleaning the carburetor or throttle body using an OBD II scanner or code reader

More complex problems to check for:

Inspect the engine intake system to ensure that everything is properly sealed and linked, as well as for leaks.

  • Check for leaks and cracks in the gaskets that seal the space between the plenum and the gasket heads. After attempting to identify these sorts of problems on your own, you might take your vehicle to a professional technician for further examination
  • However, this is not recommended. Seal for the purge valve: If your engine is making a harsh noise, it is possible that you have a big leak, which is causing the P0171 signal. Check for a faulty seal on the purge valve, as well as any other problems.

How to test for leaks:

  • If you believe there is a leak in the carburetor or throttle body, spray carburetor or throttle body cleaner around the region where the leak is suspected. The engine will either run smoother or rougher as a result, which might assist you in determining where the leak is situated. While you are spraying, have someone keep an eye on the gauges for you: If the gauges begin to vary, this is still another clue that should assist you in locating the leak. Graph the speed of your engine: While spraying carburetor cleaner on the intake gasket or surrounding region with your scan tool or code reader, you may keep an eye on the reader for any changes in engine speed. Look for a leak in the area where you’re spraying at the time of the shift in the graph’s revolutions per minute
  • If the graph decreases or spikes in revolutions per minute while you’re spraying, stop spraying immediately and investigate.

Other leaks to check for

Check for leaks in your exhaust pieces, such as the exhaust manifold, gasket, and flexible pipe, as well as the rest of your vehicle.

Low fuel rail pressure and plugged or blocked fuel injectors, filters, or pump

  • Fuel rail: Check the pressure in the fuel rail. This indicates that your vehicle is not receiving the amount of gasoline it requires, which might result in a P0171 code being shown on the dash. Fuel injectors, fuel filters, or a fuel pump: Make that none of these components are clogged or obstructed, since this would prevent the proper quantity of gasoline from reaching the engine.

Bad oxygen sensors

O2 sensors keep track of any unburned fuel or unburned fuel that makes its way into the exhaust. It is possible that an oxygen sensor is not giving the right signal to the computer, which will result in a problem and a code of P0171 to be shown.

Other sensors to inspect

Check for malfunctioning coolant temperature sensors as well as other engine monitoring sensors.

How do you fix code P0171?

P0171 codes are caused by several problems that can be fixed by the owner. If you’ve identified the problem that’s producing the code but it isn’t something you can solve on your own, you’ll need to take your automobile to a professional to get it fixed. When it comes to diagnosing and repairing automotive problems, it is critical to stay inside your comfort zone. If the problem has a straightforward solution that you are confident you can complete on your own, such as reconnecting a disconnected hose, check to see that your Check Engine light turns off after you have completed the task, that your car’s rough idle has disappeared, and that everything appears to be functioning normally.

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When you view our most recent films, you will learn about different check engine and problem codes.

Up next

Following are some blog entries to check out:

  • In this article, we will discuss what OBD-II is and how it works. What Exactly Is An O2 Sensor? What Is the Definition of Fuel Injection? What Is the Process? 6 Things Shady Mechanics Don’t Want You to Know About Their Business

Need any of the parts mentioned in this article?

  • Engine components
  • Oxygen sensors
  • Mass air flow sensors
  • Air filters
  • Engine gaskets
  • Exhaust components
  • Exhaust manifold
  • Exhaust flex pipes
  • Mufflers and exhaust components
  • Fuel system components
  • Fuel injectors
  • Fuel filters
  • Fuel pumps and assemblies
  • Coolant temperature sensors

Code P0171 – System Too Lean: Symptoms, causes, common problems, diagnostic

The most recent update was made on July 10, 2021. It signifies that the engine air-fuel mixture is too lean, or that there is too much air and not enough fuel, according to the OBDII fault codeP0171 – System Too Lean (Bank 1). Driving a car with the code P0171 can cause greater damage to the engine over time, since when the engine runs lean, the combustion temperature is higher, which can lead to additional damage.


It is possible for an engine to stall when the automobile has come to a complete stop at a stop sign when the engine is running low. It is possible that the acceleration will appear to be sluggish. It is possible that the engine will run rough at idle. Depending on whether this code is caused by a vacuum leak or not, a hissing noise may be heard coming from the engine. More information about vacuum leaks may be found here. It is also possible that the engine will be difficult to start. Engine knocking or detonation (pinging) under load or when going uphill are two more signs that the engine is running too lean.


The following are examples of common causes:-Vacuum leaks – A clog or a defective valve PVC valve or other sections of the PCV system that are faulty – Purge valve or solenoid that is stuck open – Mass Air Flow Sensor (MAF) The oxygen sensor was faulty, and the aftermarket intake was improperly placed.

– Insufficient fuel pressure; clogged catalytic converter.

How the code P0171 is diagnosed:

The diagnosis of the code P0171 is quite straightforward if you have a competent scan tool that displays live data. Without an ascan tool, the only way to determine the source of the problem is to go back to the fundamentals and look up frequent problems associated with your specific car’s make, year, and model. Please continue reading since we have done some research and provided some typical faults for various autos. A dealership is the ideal location to take your automobile for diagnostics since its technicians are factory-trained and knowledgeable about the usual problems that occur with the vehicles they repair.

  1. Any cracks in the intake boot, do you think?
  2. When driving at idle and at higher rpms, check the Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT) readings on your scan tool to make sure everything is working properly (read more about fuel trims below).
  3. If the STFT increases by more than 15-20 percent at idle but reduces by the same percentage at higher rpms, you most certainly have a vacuum leak.
  4. If the STFT increases to 15-20 percent at higher rpms, it might indicate a defective mass air flow sensor, blocked catalytic converter, or a low fuel pressure (bad fuel pump).

What is Intake or Vacuum leak?

An air leak that occurs somewhere between the engine’s intake and the mass air flow sensor is referred to as a ‘vacuum leak’ or a ‘intake leak,’ respectively. A ripped or broken intake boot, leaky intake manifold gaskets, a stuck-open or malfunctioning PCV valve or a shredded PCV hose, a cracked or disconnected vacuum line are all instances of vacuum leaks that can occur. Continue reading:Vacuum leaks: frequent causes, symptoms, and solutions. Some instances of intake or vacuum leaks include the following:

Common problems causing the code P0171 in different cars:

Searching for technical service bulletins for your particular make and model is one method of discovering a typical problem with your vehicle (TSBs). A leaky intake manifold gasket in subfreezing temperatures, according to the Toyota Technical Service Bulletin (TSB) EG045-07 for the 2003-2008 Toyota Corolla and Matrix with the 1ZZ–FEengine, is one probable cause of the code P0171, among other reasons. If the leaking manifold gasket is determined to be the result of the diagnostic procedures, the gasket must be replaced.

  1. Ford has published a technical service bulletin in response to this situation.
  2. This is a well-known problem with Ford vehicles.
  3. In many BMW automobiles, a fractured or torn intake boot is a typical cause of the code P0171, which is shown.
  4. Another Ford Technical Service Bulletin for a variety of Ford cars from the late 1990s details a problem with MAF sensor contamination in which both codes, P0171 and P0174, might display simultaneously.
  5. Sometimes the mass air flow sensor simply becomes dusty, resulting in erroneous air flow measurements and the engine operating at a lean state.

It is possible that cleaning the air flow sensor could assist temporarily; however, the true solution will necessitate replacing the malfunctioning mass air flow sensor. A scan tool may be used to evaluate a mass air flow sensor; further information can be found here: mass air flow sensor.

Basic car knowledge:how the air/fuel ratio is adjusted

Diagram of the Fuel Trim Control Modern automobiles equipped with the OBD-II system have a front oxygen sensor that measures the amount of oxygen in the exhaust gases and sends a feedback signal to the engine computer (PCM) indicating whether the air-fuel mixture entering the engine is lean (too much air and not enough fuel) or rich (too much fuel and not enough air) (too much fuel and too little air).

Accordingly, the PCM adjusts the fuel supply in order to maintain the air/fuel ratio at its optimal level, which is 14.7/1.

This is a constant process: when the oxygen sensor detects an excessive amount of oxygen, the PCM thinks that the air/fuel combination is lean and increases the amount of fuel.

In technical jargon, this modification is referred to as fuel trimming.

What isFuel Trim?

Short-term reduction in fuel consumption (STFT) A few minutes after a cold start, the front oxygen sensor is warmed up, and the engine computer (PCM) begins cycling the air/fuel ratio between a little lean and a little rich. It is estimated that this cycle occurs once or twice every second. Short-term fuel trim is the phrase used to describe this modification in the air/fuel ratio (STFT). Air fuel ratio (oxygen sensor) cycling may be seen on the graph here: air fuel ratio (oxygen sensor). In the Live Data mode, a common scan tool displays the STFT as a percentage denoted by the letters “-” or “+.” Consider the following scenario: if your automobile had a slight vacuum leak, you would see the STFT increasing by 10-15 percent at idle and decreasing by 3-5 percent at higher rpms.

For example, if the engine progressively develops a minor vacuum leak over time, the engine will operate more efficiently as a result (more air and less fuel).

In a scan tool, the long-term fuel trim is also presented as a percentage with a “-” or “+” symbol to indicate that it is negative or positive.

How thecode P0171 is set

Depending on which cylinder bank is affected, the engine computer (PCM) will illuminate the “Check Engine” light (MIL) and set the trouble code P0171 – System Too Lean for Bank 1 and (or) P0174 – System Too Lean for Bank 2 if the air-fuel mixture becomes too lean and the engine computer (PCM) is unable to compensate for this condition by adding fuel. The PCM also retains the freeze frame of the parameters (engine temperature, vehicle speed, fuel trim readings, and so on) that were present at the moment the code was entered into the computer.

Code P0171 is often triggered when either the short term fuel trim (STFT) or the long term fuel trim (LTFT) adjustment exceeds a predetermined value (typically +25 percent) in the engine control module. More information about the frozen frame may be found here.

What does the term “Bank 1” mean?

In a V6 engine, Bank1 and Bank2 are the primary banks. A different group of engine cylinders is denoted by the designations “Bank 1” and “Bank 2.” The majority of in-line 4-cylinder engines have only one bank, which is called Bank 1. V6 and V8 engines, as well as certain 4-cylinder engines, are “divided” into two groups of cylinders; the Bank 1 group of cylinders is the one that contains cylinder number 1. For further information on which is Bank 1 and which is Bank 2 in your automobile, you may consult your repair manual or Google it, being sure to include the model year, make, and engine size of your vehicle.

A: The code P0171 in the 2002 Corolla is frequently caused by a defective or filthy mass airflow sensor, as well as vacuum leaks.

If the mass airflow sensor is the source of the lean situation, cleaning it may be beneficial, but it is more often than not necessary to replace it.

What Do P0171 and PO174 Mean?

An engine with two banks, Bank1 and Bank2. A separate group of engine cylinders is denoted by the words “Bank 1” and “Bank 2.” The majority of in-line 4-cylinder engines have only one bank, which is known as Bank 1 or Bank 2. In V6 and V8 engines, as well as certain 4-cylinder engines, the engine is “divided” into two groups of cylinders; the Bank 1 group of cylinders is the one that contains cylinder number 1. For further information on which is Bank 1 and which is Bank 2 in your automobile, you may consult your repair manual or Google it, being sure to include the model year, make, and engine size of your vehicle in your search.

A: A: A malfunctioning or filthy mass airflow sensor, as well as vacuum leaks, are common causes of the code P0171 in the 2002 Corolla.

If the mass airflow sensor is the source of the lean situation, cleaning it may be beneficial; nonetheless, it is more often than not necessary to replace the sensor altogether.

P0171 and P0174 Symptoms

There are several cases where engine performance concerns do not manifest themselves. Some lean circumstances, on the other hand, might cause your car to have the following performance issues:

  • Intense or hesitant acceleration
  • Misfires (which will generally result in the generation of a misfire code)
  • Low power
  • Rough starting and idling. Spark knock or explosion.

Most of the time, you’ll only get notified if there’s a lighted CEL in the vicinity. Look for one of these typical reasons to figure out how to fix the problem code you’re having. The first thing to check is whether or not there are any additional codes present. If either code (or both codes) come at the same time as, for example, a Mass Airflow Sensorcode, it is reasonable to believe that the MAF sensor is the source of the lean state in question.

Unless one of the codes (P0171 or P0174) appears by itself, or if both codes are saved, you have an issue that necessitates more detective work. You must go beyond sensors and other components monitored by the engine’s computer to find the source of the problem.

Common Causes

There are a variety of minor and significant fixes that might result in this problem. Start with the simplest difficulties and work your way through the list until you’ve identified the root cause of your error code. Lean situations are frequently created by air entering the system in an area where it cannot be seen or measured. The intake system, which is normally behind the MAF sensor, and a vacuum leak anywhere in the intake system are the two most likely culprits for this. Starting with the intake boot that connects the MAF to the throttle body, look for any leaks.

  1. Check all of the vacuum hoses on the engine for cracks or breaks in the hose before continuing.
  2. This is a common sign of a large vacuum leak and should be addressed immediately.
  3. If nothing appears to be wrong here, it is possible that there are other, more serious problems going on.
  4. This will result in a significant vacuum leak and the onset of a lean situation.
  5. It is crucial to remember that, in most cases, fuel-related difficulties such as these will also result in a misfire code being displayed – either randomly or on specific cylinders.

How to Fix P0171 and P0174

While extensively scrutinizing the intake boot, another alternative is to stop at the MAF sensor itself for a few minutes. MAF sensors can become filthy or greased over time, causing them to send out a misleading signal. However, this is often signaled by a MAF issue code. If you utilize oiled air filters that have an excessive amount of oil on them, particles will stick to your MAF sensor, which will result in a poor performance. Once you’ve located your sensor, you may remove it and clean it using MAF cleaning spray, which you can purchase at AutoZone for a reasonable price.

A vacuum diagnostic gauge may be connected and utilized at this time, or a professional shop can assist you at this point as well.

Once you’ve identified the problem and repaired or replaced the necessary component, check your vacuum and reset your trouble code to see if you’ve resolved the problem or whether you need to hunt for more vacuum leaks.

P0171 Code: Air-Fuel Ratio Too Lean (Symptoms, Causes, and Fixes)

The most recent update was made on November 2, 2021. In order for your engine to work properly, it must have the proper fuel-to-air ratio. Your combustion engine will not perform as effectively or as efficiently as it could if there is either too much or not enough oxygen. Are you looking for a reliable online repair manual? The top five choices may be found by clicking here. When there is an excessive amount of air entering the chambers, your car will save the code P0171. A multitude of factors, ranging from a broken sensor to a problem with your fuel pump or vacuum system, might contribute to this spike in oxygen levels in your vehicle.

More information on identifying the source of code P0171, understanding how it could affect your car, and correcting the problem can be found by continuing to read this article.

What Does Code P0171 Mean?

P0171 is an OBD-II trouble code that has a description. System Is Far Too Sparse (Bank 1) A P0171 error number indicates that the air-to-fuel ratio entering your engine block is not optimal. This code is often caused by two primary faults. There is either too much air or not enough gasoline in the lines, which prevents the proper ratio from being achieved. When there is an excessive amount of air in the line, it is common to discover a vacuum leak, which allows an excessive amount of oxygen into the line.

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The second situation might suggest that your fuel pump is malfunctioning or that your fuel injectors are defective.

If there is an excessive amount of fuel in the tank, the engine will run rich.

Symptoms of Code P0171

It’s possible that when your check engine light illuminates, you won’t notice any difference in the way your car functions at first. When the light illuminates in conjunction with a P0171 code (after performing a problem code scan), there will be additional symptoms. When there is an excessive amount of air in your engine, it will not perform as well as it should. When your engine is running but you aren’t driving, you may notice a rough idle or the engine producing a coughing sound. If this is the case, call your local mechanic.

It’s possible that you’ll hear or feel your engine misfire.

These components are prone to failure. However, even if there are no additional indications, it is necessary to ensure that the components around the sensor are in proper functioning order. You don’t want to waste money by replacing a costly component without a good cause.

Causes of Code P0171

When your vehicle’s check engine light illuminates, you may not notice any differences in the way it runs. This is common. In addition to the light, there will be further symptoms when the P0171 code is encountered (after scanning for issue codes). In the event that there is an excessive amount of air in your engine, it will not operate properly. Your engine may make a coughing sound while it is running but you are not driving. If your engine is running but you are not driving, you may notice a rough idle.

If your engine misfires, you may even hear or feel it.

The failure of these components occurs.

Changing a pricey part for no apparent reason is not something you want to do.

Is Code P0171 Serious?

You should always take the information from your check engine light carefully whenever it appears on your dashboard. This regulation applies to all codes, including the P0171 code. When this code is stored in the engine, you should avoid driving your car over long distances, if at all. When your engine is running lean, there isn’t enough fuel in the tank to allow it to run at peak performance. The vehicle may become unable of accelerating in order to keep up with traffic speeds or climbing a steep slope as a result of this condition.

The code P0171 is more likely to be received by those who have modified their turbocharged car by raising the boost.

When your car displays the code P0171, it is most likely because it is not utilizing its fuel effectively.

How to Fix

To clear a P0171 error code, you’ll need to follow a few simple diagnostic and repair procedures. If you follow the procedures in the correct order, you will almost certainly be able to identify the problem. First, make sure there are no other codes in your automobile. Afterwards, you may go to work on this project. The first step is to check for leaks in the vacuum system. You may check the vacuum pressure with a vacuum pressure gauge, or you can listen around the engine for any peculiar hissing noises.

During this stage, be sure to inspect the fuel filters and injectors as well.

If there are no additional issues, this is your final step.

P0171 Diagnostic Code – Trouble Code Diagnosis Guide

System Too Lean (Bank 1); this difficulty code is frequently associated with the P0174 error code. This is one of the most often encountered fault codes in engines with V-6 or higher displacements. Specifically, the P0171 code indicates that the “System Too Lean (Bank 1)” condition has been detected by the first exhaust oxygen (02) sensor (also known as the upstream 02 sensor) on the engine’s “Bank 1” side (designated as whichever side has cylinder number one). A 14.7:1 air-to-fuel ratio is sought by nearly all Toyota gasoline engines, and O2 sensors are used to achieve this aim by detecting the quantity of oxygen in the exhaust stream.

When there is too much oxygen in the mixture, the ECM compensates by increasing the amount of fuel delivered to the engine.

P0171 is frequently activated in conjunction with P0174, which is activated when the Bank 2 sensor detects an excessive amount of oxygen in the exhaust.

Troubleshooting P0171 Code

A P0171 code often indicates that your Toyota is experiencing issues with a dirty or defective mass airflow (MAF) sensor, or that there is a vacuum leak downstream of the MAF sensor (perhaps in the PCV line or in the valve itself). Of fact, this signal might also indicate a malfunctioning oxygen sensor in bank 1. Additional factors that might cause a P0171 code to be set include: A clogged or filthy fuel filter that causes low fuel pressure, or even an exhaust leak prior to the first oxygen sensor (although this is extremely unusual).

  • In the vast majority of cases, cleaning the MAF sensor and the lines leading to and from it will be sufficient to resolve the P017 error code. This will frequently address the problem
  • When you clean the MAF sensor, make sure to check all of the lines, including the vacuum and PCV hoses, to ensure that they are free of debris. Check for kinks, cracks, and other flaws in the lines and replace them as necessary. Additionally, be sure to inspect all of the connections and hoses on the air intake, as well as the intake manifold, for leaks. In conclusion, changing your air and fuel filters is always a good idea, especially if they’re going to expire anyhow

The O2 sensor on bank 1 may need to be replaced if cleaning and checking the sensor and lines are ineffective in solving the problem. Consult your Toyota’s owner’s handbook for the precise position, which varies depending on the model. If it doesn’t work, it’s likely time to seek the assistance of a specialist. Check out this page on the Toyota Parts Blog for a full list of issue codes. While every effort has been taken to ensure the accuracy and quality of this problem code summary, we cannot be held liable for any errors or omissions in the information provided.

P0171 Code – Meaning, Causes, Symptoms (& How To Fix It)

When the Oxygen sensor on bank 1 detects a lean air-fuel combination that is too lean for the sensor to adjust, the P0171 code is shown in the engine management unit. This error code might be caused by a variety of different factors. Listed below is the information you need to know about the P0171 code.

Code Definition

P0171 – The system is running too lean (Bank 1)

What does the P0171 code mean?

The P0171 code indicates that the Oxygen (O2) sensor on bank 1 has detected a toolean mixture and has corrected the problem. The Oxygen O2 sensors have the capability of correcting a fuel mixture that is within a 15% tolerance. It will save the P0171 code if the air-fuel combination has to be corrected more than once in this manner.

P0171 Symptoms

If the fuel mixture is somewhat lean, you may not experience any further symptoms from the P0171 code other than the check engine light on your dashboard, which indicates that the code has been set. If you have an extremely lean fuel mixture, you may have any of the following symptoms:

  • It is possible that the engine will die while driving if the check engine light is illuminated, the engine is running rough or accelerating too quickly, the engine is losing power, and the engine is misfiring.

How serious is the P0171 Code?

A moderate lean mixture is one that has a substantial effect on the engine’s performance, but you will not notice any change in the engine’s performance the majority of the time. It’s possible that your car’s engine is operating at such a low state that your engine parts are in risk while under heavy load. It might be the first indicator of anything more serious that will break sooner rather than later, such as a blocked fuel filter or a faulty fuel pump. It is acceptable to drive a short distance to the workshop, but continuing to drive while the code is displayed may result in damage to critical engine components and components.

P0171 Causes

The P0171 indicates that there is a lean air-fuel mixture present, but it does not specify what may be causing the lean air-fuel combination to exist.

Actually, there are other factors that might contribute to a lean combination. The P0171 error code can result in any of the following problems:

  • Air intake/vacuum/boost pipe leak (the most frequent)
  • Faulty PCV valve
  • Low fuel pressure (caused by a broken fuel pump, filter, or fuel pressure regulator)
  • Faulty PCV valve A defective EVAP purge valve
  • Faulty O2 sensors
  • Faulty EGR valve
  • Faulty MAP/MAF sensors
  • An exhaust leak (prior to the front O2 sensors)
  • A bad coolant temperature sensor
  • Faulty sensor wirings
  • A faulty ECM/PCM (rare)
  • And a problematic EVAP purge valve.

What repairs can fix the P0171 code?

Because there can be so many various reasons of the P0171 error code, there are many possible remedies available. The following are the most often seen solutions for the P0171 error code. The most frequently encountered from the top.

  • Replace any worn or damaged vacuum hoses or gaskets surrounding the intake manifold. Other intake leaks should be repaired. Replace the PCV valve, as well as the fuel pump, fuel filter, and fuel pressure regulator, if necessary, and fix wiring. In addition to replacing the EVAP valve, the O2 sensor(s), replacing the EGR valve, replacing the MAP/MAF sensor, repairing exhaust leaks, and replacing the coolant temperature sensor, Identify and repair damaged wiring
  • Replace the ECM/PCM (this is an uncommon occurrence)

Common Diagnosis mistakes

A typical diagnostic blunder is to begin replacing parts before completing a thorough diagnosis of the problem. A vacuum leak or a faulty PCV valve are the most common causes of the P0171 error code in the vast majority of situations. If you start changing MAF sensors, oxygen sensors, and other sensors, you will most likely wind up spending a lot of money without seeing any benefits. When the P0171 code appears, a malfunctioning oxygen sensor is not a very common reason, despite the fact that many people immediately replace the sensor when they see it.

How to diagnose the P0171 Code

When you have the correct tools, diagnosing the P0171 error code is straightforward. It is frequently difficult to diagnose the P0171 without the use of these techniques. This tutorial is intended for professionals who have access to these software programs. If you ask nicely, you will most likely be able to borrow these tools from a workshop.

  1. Connect an OBD2 scanner to your vehicle’s diagnostics port. Make a second pass through the fault codes, looking for any other related trouble codes that might be causing the lean mixture. If you receive any other issue codes, proceed with the diagnosis method as described above. Assess live data from the MAF sensor and temperature sensors to see whether their readings are logical or significantly out of range
  2. Connect an EVAP smoke machine to the inlet of your vehicle and examine it for any intake leaks. Examine the PCV valve and the EVAP purge valve for any problems. A leak or a malfunctioning one-way valve will be discovered in the majority of situations as the source of the P0171 code. Check the gasoline pressure in the tank. Connect a fuel pressure gauge to the fuel rail and check to see that the fuel pressure is within acceptable limits. The fuel filter, fuel pump, fuel pressure, and regulator should all be checked if the fuel level is too low. Make that the EGR valve is working properly. An EGR valve that is jammed open might cause the air-fuel mixture to remain lean for an extended period of time. While you are opening and closing it with your diagnostic tool, attempt to inspect the valve inside it if at all possible. Make sure the MAF sensor is clean. The air-fuel mixture might be caused by a clogged MAF sensor. Examine it and look for any dirt or debris on the sensor. Following that, you should attempt to clear the issue codes and see if the code reappears. Alternatively, it might be damaged, so verify its values at idle and under pressure and replace it if necessary. Before installing the O2 sensor, inspect the exhaust pipe for leaks. If you discover any leaks, you should repair them immediately. If the problem persists and you have not discovered any problems with the items listed above, it is time to get your O2 sensor diagnosed. If you discover that it is providing incorrect values, replace it.

Estimated Repair Cost

The following are some samples of the repair expenses associated with the P0171 code. Parts and labor are included in the pricing listed. It does not cover the price of diagnostic testing.

  • Replacement of a vacuum hose costs between $10 and $50
  • Replacement of an oxygen sensor costs between $200 and $300
  • And replacement of a PCV valve costs between $20 and $60.

How to fix the P0171 code?

Check and repair vacuum leaks, correct low fuel pressure, and replace any malfunctioning sensors that might result in a lean mixture on bank 1 in order to resolve the P0171 error and get your car running again.

What causes P0171 code?

Low fuel pressure, a malfunctioning PCV valve, and a faulty MAF sensor are the most typical reasons of the P0171 code. Other causes include vacuum or intake leaks. Other factors can potentially contribute to the P0171 error code.

What does P0171 mean?

The P0171 code indicates that the O2 sensor on bank 1 detected a lean mixture and reported it. In order for the sensor to function properly, the mixture must be within +-15 percent of the target range; if it is outside of this range, the p0171 code will be saved.

How to clear code P0171?

An OBD2 scanner is required in order to clear or reset the P0171 error code. It’s important to remember that simply resetting the code will not solve the problem that caused it in the first place, and it will almost certainly reappear. Do you require a maintenance manual? Investing in a decent repair manual will save you both time and money in the long run. Take a look at the most suitable alternatives here. Magnus is the proprietor of MechanicBase and the primary creator of the website. In his more than 10 years as a mechanic, the bulk of which have been spent specializing in sophisticated diagnostics and troubleshooting, he has gained valuable experience.

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