Automobile & Light Truck Certification Test A5 BrakesAnti-lock Brake System (ABS) Diagnosis and RepairHard
A vehicle with an ABS warning light and a C0060 fault code (Left Front Wheel Speed Sensor Signal Incorrect) has been brought into the shop. Live data shows the left front wheel speed sensor outputting a consistent square wave signal at 15 Hz while the vehicle is stationary, but all other wheel speed sensors show 0 Hz. What is the MOST likely cause of this specific symptom?
- AA damaged tone ring on the left front wheel.
- BA faulty ABS control module input circuit.
- CAn internal short to power in the active wheel speed sensor.
- DA corroded wheel speed sensor connector.
Show answer & explanationAnswer & explanation
Correct answer: C. An internal short to power in the active wheel speed sensor.
An active wheel speed sensor, when faulty, can sometimes output a 'stuck high' or 'ghost' signal even when stationary, due to internal electronic failure or a short to its power supply. This constant, albeit incorrect, frequency contradicts the stationary state and points to an internal sensor issue rather than a tone ring or wiring problem.
Why the other options are wrong
- A. A damaged tone ring would cause an erratic or absent signal once the wheel starts moving, but it cannot generate a signal when the wheel is stationary.
- B. A faulty ABS control module input circuit might misinterpret a signal or show no signal, but it's less likely to *create* a consistent, incorrect frequency from a stationary wheel.
- D. A corroded connector would typically cause an intermittent or absent signal, not a consistent, incorrect frequency while stationary.
Active WSS Stuck Signal
An active (powered) wheel speed sensor that outputs a false, consistent signal (e.g., a constant frequency) even when the wheel is stationary. This is typically due to an internal electronic fault or a short within the sensor itself.
- Occurs with active (powered) sensors.
- False signal generated when stationary.
- Indicates internal sensor failure or short.
Memory trick: Still Wheel, False Pulse: Sensor's Lies!