ASE G1 Auto Maintenance and Light RepairBrakesMedium
A customer complains that their vehicle's ABS warning light illuminates intermittently, especially when driving over rough or bumpy roads. The technician retrieves no stored Diagnostic Trouble Codes (DTCs) from the ABS module. Which of the following is the MOST likely cause?
- ALow brake fluid level in the reservoir
- BA seized brake caliper on one wheel
- CA faulty ABS hydraulic control unit
- DAn intermittently open wheel speed sensor circuit
Show answer & explanationAnswer & explanation
Correct answer: D. An intermittently open wheel speed sensor circuit
Intermittent ABS warning lights on bumpy roads, especially with no stored DTCs, often point to a loose connection or damaged wiring in a wheel speed sensor circuit that momentarily loses connection over vibrations.
Why the other options are wrong
- A. Low brake fluid typically triggers the brake system warning light (red), not specifically the ABS light (amber/yellow), and would not be intermittent on bumps.
- B. A seized brake caliper would cause dragging, pulling, and potentially overheating, but is unlikely to directly trigger an intermittent ABS light on bumpy roads without other symptoms or DTCs.
- C. A faulty ABS hydraulic control unit would likely set a hard DTC and cause a continuous light, not an intermittent one triggered by bumps.
Intermittent ABS Faults
ABS warning lights that appear sporadically, often triggered by specific conditions like bumps or turns, usually indicate a loose electrical connection or damaged wiring within the wheel speed sensor circuit.
- Often related to wheel speed sensors or wiring
- Triggered by vibrations or movement
- May not always store a permanent DTC
Memory trick: Bumpy Road, Flickering Light, Check the Wires, Make it Right!