Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsGauges, Warning Devices, and Driver Information Systems Diagnosis and RepairHard
A technician is troubleshooting a vehicle where the ABS warning light is illuminated. A scan tool retrieves DTC C0034, indicating a 'Right Rear Wheel Speed Sensor Circuit Malfunction'. When checking the sensor circuit with an oscilloscope, the technician observes a square wave signal from the sensor, but it is inconsistent and drops out intermittently. What is the most likely cause?
- AA short circuit within the wheel speed sensor wiring.
- BA faulty ABS control module.
- CContamination or damage to the wheel speed sensor tone ring.
- DAn open circuit in the wheel speed sensor power supply.
Show answer & explanationAnswer & explanation
Correct answer: C. Contamination or damage to the wheel speed sensor tone ring.
If the sensor is producing a signal (square wave), it indicates it has power and is generally functioning, but the inconsistency and dropouts suggest an issue with its input. Damage or contamination to the tone ring (e.g., missing teeth, debris) would directly cause an inconsistent or intermittently missing signal, leading to the DTC and ABS light.
Why the other options are wrong
- A. A short circuit in the wiring would likely result in a constant voltage, no signal, or a distorted signal, not an inconsistent square wave that drops out.
- B. A faulty ABS control module could cause the light to illuminate and set a DTC, but if the oscilloscope shows a signal (albeit inconsistent) at the sensor, the issue is more likely upstream of the module's processing.
- D. An open circuit in the power supply would result in no signal whatsoever from the sensor, not an inconsistent square wave.
Inconsistent Wheel Speed Signal
An inconsistent or intermittently dropping out wheel speed sensor signal (square wave) often indicates contamination or physical damage to the tone ring, affecting the sensor's ability to accurately read wheel rotation.
- Sensor signal originates from tone ring interaction.
- Damage/debris on tone ring disrupts magnetic field pulses.
- Oscilloscope reveals signal integrity issues.
Memory trick: Inconsistent 'SQUARE' wave, 'TONE' ring is 'SICK'.