Automobile & Light Truck Certification Test A5 BrakesAnti-lock Brake System (ABS) Diagnosis and RepairMedium
A vehicle's ABS warning light is on, and the scan tool indicates a C0050 fault code for 'Left Rear Wheel Speed Sensor Supply Voltage'. A multimeter test at the sensor connector shows 0 volts on the supply wire with the ignition on. All other wheel speed sensors are functioning correctly. Which of the following is the MOST appropriate next diagnostic step?
- ABleed the brake system at the left rear wheel.
- BReplace the ABS control module.
- CReplace the left rear wheel speed sensor.
- DInspect the wiring harness for an open circuit or short to ground between the ABS module and the left rear sensor.
Show answer & explanationAnswer & explanation
Correct answer: D. Inspect the wiring harness for an open circuit or short to ground between the ABS module and the left rear sensor.
A C0050 code for 'supply voltage' combined with a 0-volt reading at the sensor connector indicates that the sensor is not receiving the necessary power. Since other sensors are working, the issue is isolated to this specific circuit. The most logical next step is to trace the supply wire for an open circuit (no power reaching the sensor) or a short to ground (power being diverted before reaching the sensor).
Why the other options are wrong
- A. Bleeding the brake system is a hydraulic procedure and has no bearing on electrical supply voltage to a wheel speed sensor.
- B. Replacing the ABS control module is a last resort; the fault is specific to one sensor's supply, not the entire module's output.
- C. Replacing the sensor is premature; the problem is lack of power to the sensor, not necessarily the sensor itself.
Wheel Speed Sensor Supply Voltage Diagnosis
Troubleshooting a diagnostic trouble code (DTC) indicating a problem with the electrical power supply to a wheel speed sensor.
- Often involves checking voltage at the sensor connector.
- 0 volts on the supply wire points to wiring issues or module output failure.
- A common next step is to inspect the wiring harness for opens or shorts.
Memory trick: No power to the sensor? Trace the wire, don't just replace!