Why does the ABS light come on after vehicle inspection?
3 Answers
The reasons why the ABS light comes on after vehicle inspection: Air in the system pipeline; computer system failure; vehicle speed sensor failure; ABS wiring harness breakage; poor contact of the ABS relay. How ABS works: During braking, the ABS quickly determines the wheel lock-up state based on the speed signals from each wheel speed sensor, closes the normally open input solenoid valve on the wheel that begins to lock up, and keeps the braking force unchanged. If the wheel continues to lock up, the normally closed output solenoid valve is opened, and the braking pressure on this wheel rapidly decreases due to the pipeline directly connected to the brake fluid reservoir, preventing the wheel from completely locking up due to excessive braking force. This keeps the braking state always at the optimal point (slip rate S of 20%), achieving the best braking effect and the safest driving. The role of ABS: It maximizes the effectiveness of the brakes, shortening braking time and distance. It can effectively prevent vehicle skidding and fishtailing during emergency braking, ensuring good driving stability. It allows steering during emergency braking, providing good steering control. It avoids severe friction between the tires and the ground, reducing tire wear.
I've experienced the ABS light coming on right after an inspection. The testing line has a procedure where wheels spin at high speed on rollers to simulate slippage and trigger ABS intervention. During this, sensor signals are prone to interference, and the ECU might misinterpret wheel speed anomalies. Don't worry too much though - usually driving a few kilometers allows the system to recalibrate. Last time I took my old Bora for inspection, the ABS light stayed yellow after exiting, but it turned off after just two traffic lights. If the light remains on after driving, check for loose connections at all four wheel speed sensors or metal shavings stuck to the magnetic pickup heads.
I've been repairing cars for over 20 years, and every annual inspection season brings in vehicles with illuminated ABS lights. During roller testing, wheel speed sensors rotate several times faster than usual. Older car wiring is already not in great shape, so signal interference is quite common. Last month, there was a 10-year-old Camry whose light came on right after inspection. I hooked up the diagnostic tool and found intermittent failure in the left front wheel sensor. Upon disassembly, I discovered the dust cover had cracked, allowing metal debris to stick to the magnetic head. So don't rush to replace parts—first try cleaning the magnetic head with brake cleaner. Remember to firmly reconnect the wiring connectors for all four wheels, and that should solve the problem 80% of the time.
