Tech-Info: ABS wheel speed sensors
Do you know the difference between passiv and activ wheel speed sensors? VEMO Experte explain it!
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TECH-INFO 
Wheel speed sensors record the rotary speed and, depending on the model, the rotation direction of the wheels. Driving safety systems such as ABS (anti-blocking system), ASR (anti-slip regulation) and ESP (electronic stability programme) are controlled with this information.
Signals are sent to the control device, which initiates a control process if any deviation occurs. There are two different sensors: passive and active.
Passive sensors consist of a permanent magnet and a coil winding around it. Rotation movements are transmitted to the control device as a signal. They work without a power supply, which means that a usable signal can only be generated after a certain number of wheel revolutions.
Driving assistance systems such as ASR and ESP also require the rotation direction of the wheel to be recorded. Active sensors known as Hall sensors are used for this purpose. They are equipped with electronics to allow both, speed and rotation direction, to be measured. They do not rely on the wheel revolution and therefore also work at standstill. A bipolar cable provides the sensor with power while tapping the signal via the positive cable.
Aktiv 
Passiv
Symptoms
- The control light is permanently on
- Wheels lock when braking
- Wheels skid on unpaved or smooth roads
- Driver safety systems regulate unexpectedly while driving
- Error in error memory
Causes of failure
- Break and / or short circuit in the cable or sensor
- Corrosion at plug connection
- Heavy soiling
- Mechanical damage caused by defective wheel bearings or corroded sensor rings
Recommended by the experts
- Check passive sensors by measuring resistance
- Only check active sensors by measuring the voltage or with an oscilloscope, otherwise the sensor measuring electronics could be destroyed
| Sensor, wheel speed |
A3, TT, Altea, Leon, Golf V, Passat
| X-Ref: | 7H0 927 804 | V10-72-1056 |
| Sensor, wheel speed |
E87, E90, E92
| X-Ref: | 34 52 6 762 466 | V20-72-0499 |
| Sensor, wheel speed |
W211, C219
| X-Ref: | 211 540 30 17 | V30-72-0172 |
| Wheel Bearing Kit |
A3, TT, Leon,Octavia, Bora, Golf IV
| X-Ref: | 1J0 498 625 A kit | V10-72-8803 |
| Wheel Bearing Kit |
E46, Z4
| X-Ref: | 31 22 6 757 024 kit | V20-72-8804 |
| Wheel Bearing Kit |
Focus
| X-Ref: | 1 085 569 kit | V25-72-8800 |
