ASE G1 Auto Maintenance and Light RepairBrakesMedium
A technician is diagnosing a vehicle with an illuminated ABS warning light. After retrieving Diagnostic Trouble Codes (DTCs), they find a code indicating a 'Wheel Speed Sensor Circuit Malfunction - Front Left'. Which of the following is the MOST likely initial step in diagnosing this specific fault?
- AVisually inspect the front left wheel speed sensor and its wiring harness.
- BCheck the fluid level in the master cylinder reservoir.
- CReplace the ABS hydraulic control unit.
- DBleed the brake system to remove any air.
Show answer & explanationAnswer & explanation
Correct answer: A. Visually inspect the front left wheel speed sensor and its wiring harness.
When a specific DTC points to a 'Wheel Speed Sensor Circuit Malfunction', the most logical and cost-effective initial step is to visually check the sensor and its associated wiring for obvious damage, disconnections, or corrosion before proceeding to more complex diagnostics or component replacement.
Why the other options are wrong
- B. Checking the master cylinder fluid level is a general brake system check and not directly related to a wheel speed sensor electrical circuit fault.
- C. Replacing the ABS hydraulic control unit is a drastic and expensive step, premature without thorough diagnosis, especially when a specific sensor code is present.
- D. Bleeding the brake system is unrelated to an electrical circuit malfunction of a wheel speed sensor.
Wheel Speed Sensor Circuit Malfunction Diagnosis
Diagnosing a wheel speed sensor circuit malfunction typically begins with a visual inspection of the sensor and its wiring for physical damage or disconnections, as these are frequent causes.
- DTCs often point to a specific sensor location.
- Visual inspection is a primary diagnostic step for electrical circuit faults.
- Physical damage or corrosion can cause circuit malfunctions.
Memory trick: When the ABS light glows, start by looking where the sensor goes!