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- What is an active wheel speed sensor An active wheel speed sensor detects the presence of a magnetic field and report that presence as a digital on/off signal. When used in an anti-lock brake system, the sensor detects and alternating the north/south poles of a rotating multipole magnetic ring, usually inserted into the wheel bearing.
What is a active wheel speed sensor?
Active wheel-speed sensors are an integral part of brake control systems. They detect the rotational wheel speed of vehicles using a non-contacting measurement principle.
How does an active speed sensor work?
Active sensors require an external power source to operate and work in conjunction with a toothed or magnetic ABS ring. Active sensors create a digital signal which is transmitted to the control unit in the form of a current signal using pulse width modulation.
What is the difference between an active and a passive wheel speed sensor?
A passive sensor creates an AC signal that changes frequency as the wheel changes speed. An active wheel speed sensor creates a digital signal. This type of digital wheel speed sensor uses a hall effect or a variable reluctance signal with a square wave pattern. The sensor may have two or three wires.
How do I know if my wheel speed sensor is active?
There is no way to quickly tell if a Wheel Speed Sensor (WSS) is passive or active. Both sensors have two wires and are located in the same position on the vehicle. Often, the service information will not indicate what types of sensors are on the vehicle.
Can you drive with a bad wheel speed sensor?
In general, it is unsafe to drive a vehicle with a broken wheel speed sensor. The car’s computer will not be able to determine the speed that your vehicle is traveling, so it might apply the brakes at a faster rate than necessary or increase the engine power.
What are symptoms of a bad speed sensor?
5 Common Bad Speed Sensor Symptoms
- Transmission problems.
- Erratic speedometer readings.
- Inability to engage cruise control.
- Lack of torque converter clutch application.
- Check Engine Light is triggered.
- An internal electrical fault in the speed sensor.
- Damage on the sensor itself.
- Poor vehicle maintenance.
What happens when a wheel speed sensor goes bad?
Failing wheel speed sensors will often result in the car turning off the traction control, the stability control, or other driver assist features.
Are all wheel speed sensors magnetic?
Wheel speed sensors and how we test them have been changing. Currently, two types of wheel speed sensors are in use: magnetic inductive (passive) and magneto resistive (active).
Is a wheel speed sensor an ABS sensor?
An anti-lock brake sensor or ABS sensor is a type of tachometer that measures the rotational speed of a wheel and passes it to the car’s Engine Control Module (ECM). The ABS sensor is also called the wheel speed sensor or ABS brake sensor.
Is ABS active or passive?
Anti-lock braking systems (ABS) help prevent the wheels of a vehicle from locking when braking heavily, and enable the driver to keep steering (on slippery roads for example). ABS is one of the key active safety systems that are already widely fitted to today’s passenger cars and commercial vehicles.
What causes wheel speed sensor failure?
The reason for the failure is related to the lack of information being sent to the vehicle’s electronic control module. Without the wheel speed sensor, the computer can’t tell if the car’s wheels are locking up or not and is forced to shut down the system.
What does the speed sensor on a transmission do?
A transmission speed sensor calculates the transmission gear ratio when in use. A car has two speed sensors: the ISS and the OSS, working together to show the transmission data to the car’s powertrain module. The ISS sensor monitors the input shaft’s speed.
How long do wheel speed sensors last?
There’s no hard-and-fast rule to help you predict how long your wheel speed sensor is going to last. Unlike a brake light switch or brake caliper that can last as long as your vehicle, you can expect your transmission speed sensor to last between 30,000 and 50,000 miles.
Wheel Speed Sensors – Active and Passive
A wheel speed sensor will be involved if you are replacing a wheel bearing on a late-model vehicle. This is something you should know about. Wheel speed sensors have been shifting from differentials, axles, and knuckles to the inside or on the outside of the wheel bearing or hub unit during the last ten years. The wheel speed sensors are more precise and typically more shielded from the weather when they are installed in this location. The usual wheel bearing job may necessitate the use of a scan tool, scope, or meter to ensure that the sensor is functioning properly.
The variable-reluctance magnetic sensor is comprised of a permanent magnet pickup core and a coil that surrounds the permanent magnet pickup core.
The sensor is positioned at a precise distance from a notch and tooth reluctor ring to ensure proper operation.
The rotation of the reluctor ring causes the magnetic field between the notch and the tooth to increase and decrease, resulting in the generation of a voltage in the coil.
- With an increase in the speed of the reluctor ring, the amplitude of the voltage signal will increase proportionally.
- There are two wires that connect to the variable-reluctance sensor, which is housed in a hub unit between the bearing races.
- These magnetic rings are frequently seen on the bearing’s seal, which makes sense.
- Compared to the reluctance sensor, the capacitance sensor is more stable in high-vibration settings and performs more efficiently.
- Using an alternating magnetic pole reluctor ring that is integrated into the rubber seal, the sensor’s small size allows it to be integrated into a hub bearing with minimal space requirements.
- The sensor generates a square wave signal with a high signal of 1.93 volts and a low signal of 0.64 volts, with the high signal being the highest.
- Because the signal’s amplitude does not fluctuate, this has several advantages.
It is reasonable to charge for diagnostics because the information and scan tool are both expensive to get.
It’s possible that the problem already exists, and that there is a recognized cure that can save both time and money.
When a DTC or fault is discovered, a DVM and an oscilloscope are utilized to verify the situation.
You can get by without a scope, but you’ll need a decent digital video monitor that can measure frequency.
A wheel speed sensor wave pattern can be displayed correctly using an oscilloscope, but it is a time-consuming operation that requires a significant quantity of information to be displayed accurately.
The diameter of an ordinary automobile tire ranges from 24 to 28 inches in circumference.
The frequency of the sensor would give you an approximation of the number of teeth on the reluctor, which you could use to make adjustments.
The time basis is chosen to allow for the presentation of all of the signals produced by a single revolution on the screen.
In milliseconds (mS), this would be 0.03125 second, or 30 milliseconds (mS) rounded to the closest mS.
When the speed of the reluctor increases, the amplitude of the signal produced by an inductive sensor will alter as well.
Air gaps and high resistance connection conditions can both be indicated by low-amplitude signals.
A signal produced by a cracked, broken, or missing reluctor may not be processed by the BCM due to the nature of the signal.
The square wave signal, on the other hand, does not require any processing by the BCM because it is a direct input. When a tooth is missing, it can result in Trouble Codes C1141 through C1144. These codes can be confirmed using a scope.
Passive and Active ABS Wheel Speed Sensor Function
Wheel speed sensors are an essential component of the ABS system as well as a sensor input. Its purpose is to provide information to the ABS control module about the rotating wheel speed. Passive sensors and active sensors are the two types of sensors that may be found on today’s automobiles. Passive sensors, as they are commonly known, are made up of a magnetic pin with tiny copper wire wrapped around it to produce a magnetic field. When a toothed metal ring, known as a tone ring, passes over the sensor’s field, the polarity of the sensor changes.
- An issue with false cycling occurs when the signal is hampered by a weak sensor, a defective tone ring, or debris in the circuit.
- This classic form of PM sensor, which was comparable to those used on crankshaft and camshaft systems, had a number of drawbacks that needed to be addressed.
- A passive sensor generates an alternating current signal whose frequency changes in response to the wheel’s rotational speed.
- It keeps track of the inputs from all four wheels.
- An active wheel speed sensor generates a digital signal that may be read by a computer.
- It is possible that the sensor has two or three wires.
- It’s also capable of sensing which way the wheel is rotating at any one time.
Active Wheel Speed Sensors
Sensors for wheel speed detection measure the rotational speed of a wheel that is moving. Active wheel speed sensors can detect rotation speed down to zero, and the most recent sensors are capable of detecting the direction in which the wheel is rotating as well. At the moment, four distinct sensor designs are in use. In its basic form, a variable reluctance magnetic pickup is nothing more than a coil of wire wound around a magnet. The sensor is situated near to a target wheel known as a tone ring, which has square teeth and resembles a gear in appearance.
- As a tooth on the tone ring gets closer to the magnet, the voltage on the tone ring rises.
- As it goes away from the magnet, the voltage continues to decrease (to become negative voltage) until it exits the magnetic field, at which point the voltage returns to zero.
- Although it is an analog transmission, computers can only work with digital signals.
- A magnetic pickup is a passive sensor, which means that it creates voltage only when the wheel is going faster than a particular speed, which is commonly 5 miles per hour.
- This device detects the existence of a magnetic field and provides an electronic signal that is either yes or no in nature.
- The presence of a magnetic field with lines of flux traveling through the semiconductor (front to rear) would generate a voltage at right angles to the current when current flows through a thin flat semiconductor (from left to right).
- Because the wheel includes gaps or windows, the magnetic field is interrupted alternatively as it turns, causing the induced voltage to alternately switch on and off.
The window spacing may be represented as degrees of rotation.
Because it can detect slower wheel speeds than a magnetic pickup, it may be used to detect a reference point or even the direction of rotation.
For many years, this sensor has been employed in ignition systems; nevertheless, it is sensitive to variations in temperature as well as physical contamination.
In recent years, two additional types of active wheel speed sensors have become increasingly popular.
It was the Continental Teves Mark 20 braking system, which was debuted in the 1990s, that was the first to be capable of operating brake calipers without the driver pushing the brake pedal, as well as the first system to include active sensors.
In a similar fashion to a magnetic pickup, it is composed of wire coils wrapped around a permanent magnet.
Whenever a tone ring tooth passes by a magnet, the variations in magnetic flux generate variations in the resistance of the circuit, which in turn modifies the current flow through the circuit.
This results in the generation of digital high-low voltage signals.
Because high or low voltage is always present, wheel speed may be recognized even when the voltage is zero.
Despite the fact that it continues to detect variations in magnetic flux, this time the magnet is moving.
The sensor assembly is made up of two sensing components that are positioned side by side, as well as an amplifier chip that is integrated into the sensor assembly itself.
Aside from that, as previously stated, the high-low switching frequency is related to wheel speed, and because the signal is always present, zero wheel speed is detectable.
This is how the sensor determines the rotational direction.
If B is behind A, the wheel is turning in the opposite direction as A.
Active wheel speed sensors are now frequently included into the wheel bearing assembly.
It is not always possible to detect the dual sensing elements since they are enclosed inside the wheel bearing shell.
The versions with dual sensing elements include a ring of small magnets that resembles a roller thrust bearing. Newer models include magnets incorporated into the wheel bearing seal, which makes them more durable.
Why Active Sensors?
As of model year 2012, all light trucks will be required to have some form of Electronic Stability Control (ESC) system installed in them (see June 2007Motor Age). The Continental Teves system, which was previously described, was created for automobiles and released by Mercedes-Benz in 1995. However, the size, weight, and price of the components have decreased to the point that some manufacturers are including ESC in all of their vehicles. We are currently in the second generation of ESC technology, which is characterized by the employment of dual-element active wheel speed sensors in most cases.
Because it must be able to apply the brakes even if the driver does not depress the brake pedal, the Antilock Brake System (ABS) pump is more durable than prior generations, according to the manufacturer.
In conjunction with this feedback and wheel speed sensors that are capable of reading zero wheel speed, as well as certain programming, the braking system may hold the car in place when the driver releases the brake pedal, so offering a hill-holding function.
This feature will not be covered in detail here, as Brake Assist automatically applies full brake boost when the control unit determines that the driver is performing a panic stop.
Scan Tool Testing
It is possible to examine the wheel speed sensors while the car is being driven using a factory or upgraded scan tool. Wheel speed sensor failures on the Toyota system will result in the assignment of chassis (C) codes C0200 through C0231. Some of the codes represent circuit failures, while others are plausibility codes. Despite the fact that these sensors are capable of detecting zero wheel speed, plausibility determinations are made at speeds of 6 mph or larger in the forward direction and 1.8 mph or greater in the reverse direction, respectively.
If there is a disparity of 5 mph between the wheel speed and the vehicle speed, codes will be set.
If the ABS engages the pressure release valve at any caliper for more than 28 seconds, a plausibility code will be set in the vehicle’s computer.
Another possibility is that metal has become adhered to the sensor rotor magnets and the control unit will determine this.
Self Test Mode
The Tundra’s skid control system offers a self-test mode that allows you to test the system while driving, whether or not you have a scan tool attached to your vehicle. It is recommended that the test be carried out whenever a wheel speed sensor or wheel bearing is removed or changed. When the system is tested in self-test mode, live scan tool data as well as pass/fail indications from the instrument panel lights and warning buzzers will be generated. The test will also create fault codes, but they will be immediately deleted if the test is completed successfully and all of the parameters are met or exceeded.
- Entering the self-test mode should only be done if you are fully prepared to accomplish the task.
- Proceed to the Technical Information System to purchase a subscription (a one-day membership to TIS costs $10; a one-month subscription to TIS is $50).
- Despite the fact that this braking system was introduced first on the Tundra, we anticipate that it will eventually become Toyota’s standard brake system.
- Among the codes displayed in the self-test mode are C1271 through C1278, which denote circuit faults or metal attached to the rotor magnets, respectively.
Bare Sensor Tests
The wheel speed sensors on the Tundra are double magneto-resistive components that read data from a ring of 48 magnets that is integrated into the inner wheel bearing race of the vehicle. Although voltage is provided to the sensor over a single wire, the circuit must be complete and in excellent working order in order to provide reliable data. When the ignition switch is turned on, a reference voltage is delivered to the active wheel speed sensors, and this voltage remains constant. Those voltages are supplied by the braking system control unit, and on this specific model, they may range anywhere from 5.5 volts to a maximum of 20 voltages (yes, 20 volts, even with the engine not running).
The fact that it is a two-wire sensor and that the control unit monitors the return signal precludes the possibility of testing for reference voltage across the connection terminals. When you have the connector disconnected, look for voltage between one terminal and the chassis grounding.
Future Plans
In addition, there is one more Toyota brake system that we anticipate becoming increasingly prevalent in a few years’ time. With the new Lexus LS460, brake-by-wire is effectively implemented on top of a hydraulic braking system that is identical to the one previously described, but it also has a hydraulic booster and pressure accumulator. The “Driving Support Control Unit” can apply the brakes in an attempt to avoid a collision or reduce the severity of its consequences by utilizing vehicle data already stored on the CAN bus, as well as information from the Adaptive Cruise Control radar and various optical sensors.
Despite the fact that wheel speed sensor data is still collected by the ABS controller, that data as well as all braking functions may be combined into a more powerful control unit in the future.
Because replacing an active sensor may necessitate the replacement of a wheel bearing assembly, the equipment and information necessary for a correct diagnosis are equally important.
Active Wheel Speed Sensor Diagnostics
Among the Toyota brake systems, there’s one in particular that we predict to become increasingly prevalent in the coming years. Braking-by-wire is used in the new Lexus LS460. It is built on top of a hydraulic brake system that is identical to the one described above, but it also includes a hydraulic booster and pressure accumulator. The “Driving Support Control Unit” can apply the brakes in an attempt to avoid a collision or reduce the severity of its consequences by utilizing vehicle data already present on the CAN bus, as well as information from the Adaptive Cruise Control radar and various optical sensors.
The ABS controller continues to collect data from the wheel speed sensors; however, that data and all braking operations may be transferred to a more powerful control unit.
It is equally important to have the correct diagnostic equipment and knowledge since replacing an active sensor may necessitate replacing a wheel bearing assembly.
Testing Active Wheel Speed Sensors
To test the active speed sensor, the most effective instrument is a decent scanner, especially one that can display the data from the individual speed sensors in graphical form. A lab scope is arguably the most accurate way to get a more specific answer since it can be linked directly to the sensor and read the individual sensors or wires, rather than the complete system as with the scanner, rather than the full system. The passive speed sensor and the active speed sensor are the two “kind” of sensors that are most commonly seen on modern automobiles: passive and active speed sensors.
- More information is available by clicking here.
- With each pass of the tone ring in the magnetic field, the polarity changes from positive to negative.
- The ABS controller generates a digital signal, which is used by the newer active sensor.
- The sensor is made up of two wires: one is used to carry the positive (DC) voltage from the controller, and the other is used to carry the return (ground) voltage from the sensor to the controller.
- They are not required to create the necessary voltage themselves through the spinning movement of the wheel.
- Not only does this provide the controller with the capacity to compute wheel speed, but it may also be utilized in conjunction with the hill holding and hill descent control functions present on some cars.
- The resistors have a resistance of around 1.4k ohms apiece, but if you measured the resistance at the wire ends, you would most likely find it to be between 5 and 6 mega ohms.
It appears that the tone wheel (when smoothed down) resembles the square wave pattern that it generates.
Despite the fact that the sensor voltage is near to the battery voltage (10.6v according to what I’ve discovered), you will not be able to read it with a test light.
It is conceivable that the computer will detect a short to ground if you try to poke a test light into the positive lead leading to the sensor.
With reality, in most of these ABS systems, if you “short” the lead, the CPU will turn off the sensor (0.0v) until the next key cycle is initiated.
However, if you kept checking the circuit without turning off the key, you’d wind up back at the processor and more than likely come to the conclusion that the processor is faulty as a result.
Simply cycle the key and review your work.
A lab scope is arguably the most accurate way to get a more specific answer since it can be linked directly to the sensor and read the individual sensors or wires, rather than the complete system as with the scanner, rather than the full system.
LED Tester is a device that tests the brightness of LEDs.
Disconnect the sensor from the vehicle (Caution: Do not do this while the sensor is still connected!
In addition to the sensor, you should connect the other lead from the sensor to your resistor and LED, while the remaining lead from your LED should be connected to the battery.
(Only the LED is concerned with which direction the sensor is pointing.) As you spin the wheel, you’ll see that your LED is flashing on and off, with the blink rate rising and decreasing as the wheel speed varies.
When it comes to these sorts of sensors, your scope or scanner is the best option.
It will not test the full system, but it will determine whether or not the speed sensor is operational.
In this situation, a scanner, a scope, or a home-made LED tester can assist you in diagnosing the active speed sensors on your vehicle. Always test first, test second, and if you’re still not sure, test a third time before proceeding.
AutoFocus: Making sense of wheel speed sensors
Wheel speed sensors, as well as the methods by which we assess them, have evolved throughout time. Wheel speed sensors are now available in two configurations: magnetic inductive (passive) and magneto resistive (active) (active). Passive sensors have been in use since the inception of the anti-lock braking system in the 1970s (ABS). These are the sensors that operate on the basis of the generator concept. The sensors function in conjunction with the toothed tone wheels to monitor and send information about wheel speed to the anti-lock braking module (ABM).
- It is possible to use each tooth on the tone wheel to operate the wheel speed sensor individually.
- When a consequence, an alternating current (AC) voltage is created in the speed sensor coil by magnetic lines of force varying as the tone wheel passes past the magnetic sensor.
- Vehicle to vehicle, the output of the wheel speed sensor might differ owing to factors such as winding type, air gap, magnetic strength of the sensor, metal qualities of the tone wheel, and the speed of the tone wheel.
- This problem is more likely to occur at lesser wheel speeds than at higher wheel speeds.
- This occurs mostly as a result of tone wheel damage or rust accumulation on the tone wheel.
- Make a point of inspecting these locations.
- This sort of sensor is also used by the Teves Mark 25, Teves Mark 25e, TRW EBC-340, certain EBC-125, and some Bosch systems from the late 1990s and early 2000s.
In other words, these sensors do not appear to be affected by the false cycle problem that has plagued passive sensors for years.
The LX automobiles (Chrysler 300, Dodge Magnum, and Dodge Charger) do not have a typical tone wheel, but instead employ a magnetic encoder in place of one.
The ring is then forced on the axle shaft in the same way that a tone wheel would be.
In this system, the ABM provides battery voltage to the sensor, which allows it to be powered up.
This 7 mA signal is switched on or off depending on the position of the tone ring or magnetic encoder position.
The ABM continuously analyzes the changing digital data from each wheel speed sensor, which is then translated into wheel speed by the computer.
Normal voltage levels fluctuate between around 0.8 volts and 1.6 voltage levels as the wheel is moved in a clockwise direction.
Then there’s Teves Mark 25e to contend with.
Furthermore, the voltage fluctuates by only 0.2 volts every rotation of the wheel, making matters much more difficult!
Furthermore, all of the service information accessible at the time of publication of this post is incorrect!
A labscope may also be used to test this system, which is another option.
Then, using the channel one lead of the scope, keep an eye on the signal coming from the sensor’s power supply cable.
It is possible to discern a square-wave signal when the wheel rotates slowly over time.
Make sure you are aware of the ABS system you are dealing with, as each one requires a particular set of tests.
Another method for distinguishing active sensors from passive sensors is to look at a wiring diagram. If a sensor is labeled as “12 Volt Supply Circuit” on the wiring diagram, the sensor is part of an active wheel speed sensor system. Identifix Inc. is the source of this information.
Active Wheel Speed Sensor Diagnostics
Generally speaking, there are two “types” of sensors that are present on modern automobiles: the passive speed sensor and the active speed sensor. They both accomplish the same job, yet they operate in a completely different manner. In order to generate its own alternating magnetic field, the passive speed sensor makes use of a magnet with tiny copper wire wrapped around it. With each pass of the tone ring in the magnetic field, the polarity changes from positive to negative. The frequency of this variation is dependent on the wheel speed.
- They both accomplish the same job, yet they operate in a completely different manner.
- With each pass of the tone ring in the magnetic field, the polarity changes from positive to negative.
- The ABS controller generates a digital signal, which is used by the newer active sensor.
- The sensor is made up of two wires: one is used to carry the positive (DC) voltage from the controller, and the other is used to carry the return (Ground) voltage from the sensor to the controller.
- They are not required to create the necessary voltage themselves through the spinning movement of the wheel.
- This provides the controller with the capacity to compute not only wheel speed, but also hill holding and hill descent control, which are both available on some cars today.
- More information is available by clicking here.
The resistors have a resistance of around 1.4k ohms apiece, but if you measured the resistance at the wire ends, you would most likely find it to be between 5 and 6 mega ohms.
This group of parallel resistors works together to produce the voltage variations that you’ll notice on your lab scope as the tone wheel travels through the internal magnet.
When the high portion of the tone wheel’s tooth is close to the sensor, a greater voltage is generated, but when the low part of the tone wheel’s tooth is close to the sensor, a lower voltage is generated.
A test light is composed of three parts: a ground lead, a bulb (resistance), and the positive end, which is essentially the same as the sensor’s internal components except for the absence of magnets.
In other words, it believes your test light to be the sensor since the return voltage on the ground side of the sensor has varied dramatically during the course of the test.
As a result, there is no risk of any damage being done to the processor’s internal circuitry.
It is not the case.
Putting an Active Speed Sensor through its paces To test the active speed sensor, the most effective instrument is a decent scanner, especially one that can display the data from the individual speed sensors in graphical form.
In contrast, if you’re searching for a rapid test to verify whether or not merely the speed sensor is in working condition, you can create a simple little tester yourself in under an hour.
You’ll need a 220 ohm resistor, an LED, and a 12 volt battery supply to complete this project.
In addition to the sensor, you should connect the other lead from the sensor to your resistor and LED, while the remaining lead from your LED should be connected to the battery.
(Only the LED is concerned with which direction the sensor is pointing.) As you spin the wheel, you’ll see that your LED is flashing on and off, with the blink rate rising and decreasing as the wheel speed varies.
When it comes to these sorts of sensors, your scope or scanner is the best option.
It will not test the full system, but it will determine whether or not the speed sensor is operational.
In this situation, a scanner, a scope, or a home-made LED tester can assist you in diagnosing the active speed sensors on your vehicle. Always test first, test second, and if you’re still not sure, test a third time before proceeding.
Brake Shop: Wheel Speed Sensors
A vital component of active safety systems, wheel speed sensors measure the speed of a vehicle’s wheels. They do this by using magnetic fields to determine the rotational speed of the vehicle’s wheels in a contact-free way. In terms of operation, wheel speed sensors are categorised as either active or passive, depending on the type of sensor used. Although the categorization system appears to be paradoxical, here’s how it works: A passive sensor is a sensor that functions and provides an useable signal without the need for an external power supply voltage to be provided to it.
An active sensor is a sensor that operates and generates an output signal only when it is supplied with a voltage from a power source.
A passive wheel speed sensor is located immediately near to a toothed impulse or tone ring, and it measures the rotational speed of the wheel.
A pole pin is located inside the sensor and is linked to a permanent magnet by means of a winding that surrounds it.
With each spin, the tone ring’s alternating teeth spacing passes closer and closer to the sensor until it finally stops.
The sensor coil generates an alternating voltage as a result of the changing magnetic field.
The frequency and amplitude of the speed sensor’s signal increase in proportion to the speed of the wheel’s revolution.
A variety of factors, however, can have an impact on the quality of the data produced by a passive speed sensor.
Because the control unit may demand that the sensor signal have an amplitude greater than a specific threshold, it is possible that the sensor signal’s amplitude is just too low for the control unit to handle at low speeds.
For the second time, because the sensor is dependent on the oscillating magnetic field generated by the sensor magnet and the tone ring, the physical interaction between the two is extremely crucial.
Although the sensor gap on certain cars may be altered, this is not the case on the majority of vehicles.
If the gap is out of specification and no modification is feasible, it is likely that the tone ring or wheel speed sensor will need to be replaced.
A buildup of metallic filings on the sensor’s magnet might cause the sensor to provide an inconsistent signal or even a loss of signal.
Corrosion can seep between the components of the tone ring and cause it to malfunction.
A tooth that is missing or out of alignment might potentially degrade the quality of the signal received by the receiver.
When removing a half-shaft from a steering knuckle, never use a pry bar or a hammer to do it.
Because the sensor signal degrades as vehicle speed falls, the majority of erroneous ABS activation occurrences occur while the vehicle is traveling at a slow speed.
If an ABS activation is required, the ABS control unit evaluates the signal amplitude and frequency from all of the wheel speed sensors on the vehicle to decide whether or not the ABS should be activated.
Find the source of unpredictable, inconsistent wheel speed sensor data by inspecting the tone ring movement produced by worn wheel bearings, as well as the other components described above.
The afflicted sensor, as well as any associated wiring and connections, should be visually inspected for abnormalities if DTCs or diagnostic procedures indicate a passive wheel speed sensor failure.
If the sensor resistance is not within specification, the sensor will not be able to generate an accurate signal to the control unit.
A DC bias voltage is provided to the sensor by certain ABS control units through the ground wire, allowing the sensor to be checked by the control unit before the car is moved.
Specifically, the voltage returned by the sensor is being monitored by the ABS control unit.
It is not always the case that a defective sensor is the source of problems with these systems.
Connect the ground lead of the meter to the battery ground and the positive lead to the signal wire in order to measure the bias voltage of the circuit.
In most cases, the DC bias voltage provided to the circuit should be there even if you do not rotate the wheel.
The bias voltage supplied by the ABS module should be in the range of 1.5V to 5V at all times.
Although passive and active wheel speed sensors may appear to be identical in appearance, their operation is quite different.
In certain designs, the active sensor is similar to the variable-reluctance passive sensor in that it employs a tone ring and a permanent magnet.
One wire sends a reference voltage from the control unit, while the other wire is responsible for the sensor signal transmission.
Unlike the passive sensor, which produces an alternating current signal, changes in the electromagnetic field created by the toothed tone ring passing through the active wheel speed sensor cause the active wheel speed sensor to produce a direct current signal.
It is a proximity sensor with integrated electronics that receives a specified voltage from the ABS control unit and is used to detect objects in close proximity.
Magnets with alternating pole orientations are inserted inside the sealing ring to provide additional security.
The sensor electronics transform this sinusoidal signal into a digital signal, which is then output by the sensor.
In addition to magnetoresistive sensor elements, active sensors make use of Hall sensor elements to allow for a larger air gap and to respond to even the smallest changes in the magnetic field.
It is necessary to have an additional magnet attached to the sensor element when a steel impulse ring is used in the place of a multipole tone ring while installing the sensor element in a car.
When using this sort of sensor design, the signal accuracy is increased.
The active sensor design is similar to the passive sensor design in that the control unit calculates the wheel speed based on the frequency of the digital DC signal from the active sensor.
By eliminating tone rings, the design of the corresponding powertrain components is made simpler, and the sensitivity to electromagnetic interference is reduced to a more manageable level.
Active sensors are also less sensitive to vibrations and temperature variations than passive sensors.
DTCs (diagnostic trouble codes) are also generated by your scan tool to alert you to problems with a certain speed sensor or its circuit.
Keep in mind that active sensors provide a digital, DC square wave signal, as opposed to the analog, alternating current sine wave produced by passive sensor.
Keep an eye out for any irregularities that might indicate broken or damaged parts.
When the leads are linked in one direction, your meter may report resistance, but when the leads are connected in the other, your meter may read open circuit.
Karl Seyfert is a writer and poet. Obtain a PDF version of this document.