What causes the ABS light to illuminate on the car?
3 Answers
When the ABS light illuminates on the car, it indicates a fault in the anti-lock braking system. The function of this system is to automatically control the braking force during vehicle deceleration, preventing wheel lock-up and maintaining a rolling-sliding state to ensure maximum wheel-to-ground adhesion. The ABS light turns yellow due to faults such as wheel speed sensor failure, ABS control unit malfunction, CAN line issues, or related circuit problems. When the ABS yellow light appears, you should check: whether the grounding contact of the ABS hydraulic control device is proper; whether the wiring connectors and sockets of the ABS electronic control unit are properly connected and undamaged; and whether all relays and fuses are intact and securely plugged in.
The day before yesterday, I was driving our old Tiguan when the ABS light came on, which made me pull over immediately to check. Actually, the most common cause is dirty wheel speed sensors—there’s one behind each of the four wheels, specifically monitoring wheel rotation. Around our construction site, muddy roads are common, and splashed mud can cover the sensor probes, causing the ABS computer to lose signal and trigger a warning. Sometimes, with older vehicles, sensor aging or loose connectors can also cause the light to come on. That time, I just wiped the left front wheel’s sensor with a damp cloth, and after restarting, the light went off. But a heads-up: if both the ABS and handbrake lights come on simultaneously, it’s likely due to low brake fluid—definitely not something to take lightly.
As a mechanic with ten years of experience, I encounter the ABS warning light staying on almost every day. The root cause is that the onboard computer detects an abnormality in the anti-lock braking system and illuminates the yellow warning light. The three most common fault points are: wheel speed sensors covered with iron filings (accounting for 60% of repairs); sensor wiring damaged by rodents or connectors with water ingress (30% of cases); the remaining issues are internal electronic faults in the ABS pump module. Last time, a Volkswagen Bora had the warning light on during rainy weather. Upon inspection, we found the right rear wheel sensor wiring harness was worn through by the tire, exposing the copper wires. Such problems are not recommended for DIY repairs, as they involve the braking system. Professional diagnostic equipment is required to read fault codes for accurate troubleshooting.
