The rear ABS sensor, also known as the wheel speed sensor, is a crucial component in a vehicle’s Anti-lock Braking System (ABS). It measures the rotational speed of the wheels and transmits this information to the ABS control unit, which is essential for the ABS to function correctly, preventing the wheels from locking up during hard braking and maintaining the vehicle’s steerability and stability.
Understanding the Rear ABS Sensor
The rear ABS sensor operates based on the principle of electromagnetic induction. A toothed wheel, called the impulse ring, is attached to the brake disc or drive shaft. The wheel speed sensor, which is an inductive-passive sensor, is positioned over the impulse wheel. As the impulse wheel rotates, the magnetic field generated by the sensor’s pole pin and winding changes due to the switching from tooth to tooth space. This changing magnetic field induces a quantifiable alternating voltage in the winding, the frequency and amplitude of which are directly proportional to the wheel speed.
Measuring Wheel Speed
The frequency of the signal generated by the ABS sensor can be measured to determine the wheel speed. For instance, if the signal frequency is 1000 Hz, and there are 40 teeth on the impulse wheel, the wheel makes 40 revolutions per second, or 24000 revolutions per minute. This information can be used to calculate the distance traveled per second, and thus the speed in m/s.
Identifying Faulty Sensors
In a practical scenario, as described in a YouTube video, a faulty ABS sensor in a Porsche was identified by comparing the live data from all four ABS sensors. The faulty sensor showed a constant 0 value, while the other sensors showed the same reading, indicating that they were working correctly.
Technical Specifications of Rear ABS Sensors
The technical specifications of a rear ABS sensor can vary depending on the vehicle make and model. Here are some examples:
| Vehicle Make | Sensor Clearance |
|---|---|
| Subaru Forester | 0.7 – 1.2 mm (0.028 – 0.047 in) |
| Volkswagen Golf | 0.5 – 1.5 mm (0.020 – 0.059 in) |
| Ford F-150 | 0.4 – 1.2 mm (0.016 – 0.047 in) |
It’s important to note that the sensor clearance is crucial for the proper functioning of the ABS system. If the clearance is not within the recommended range, it can lead to sensor failure or inaccurate readings, which can affect the ABS performance.
Troubleshooting Rear ABS Sensors
When troubleshooting a rear ABS sensor, it’s essential to follow the manufacturer’s instructions and use the appropriate diagnostic tools. Some common issues that can arise with rear ABS sensors include:
- Sensor Failure: The sensor may fail due to wear and tear, physical damage, or electrical issues. In such cases, the sensor will need to be replaced.
- Sensor Misalignment: If the sensor is not properly aligned with the impulse ring, it can cause inaccurate readings or sensor failure. Ensure that the sensor is installed according to the manufacturer’s specifications.
- Wiring Issues: Problems with the sensor wiring, such as loose connections or short circuits, can also lead to sensor malfunctions. Check the wiring and connections for any issues.
- Impulse Ring Damage: The impulse ring, which is attached to the brake disc or drive shaft, can become damaged over time, leading to inaccurate sensor readings. Inspect the impulse ring for any signs of wear or damage.
To diagnose and troubleshoot rear ABS sensor issues, you can use a multimeter to check the sensor’s resistance, voltage, and frequency output. Additionally, many modern vehicles have diagnostic systems that can provide live data from the ABS sensors, which can be helpful in identifying and resolving any problems.
Conclusion
The rear ABS sensor is a critical component in a vehicle’s ABS system, responsible for measuring the rotational speed of the wheels. Its operation is based on electromagnetic induction, and the frequency of the signal generated by the sensor can be used to determine the wheel speed. Understanding the technical specifications and troubleshooting procedures for rear ABS sensors is essential for maintaining the proper functioning of the ABS system and ensuring the safety and stability of your vehicle.
Reference:
- How to get ABS LIVE DATA from your car in 2 minutes – YouTube
- BRAKE DISCS AND WHEEL SPEED SENSORS IN ABS SYSTEMS – HELLA
- Rear ABS Wheel Speed Sensor measuring questing – SubaruForester.org
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