What is the reason for the ABS light coming on after a vehicle inspection?
3 Answers
The reasons for the ABS light coming on after a vehicle inspection are: 1. Air in the system pipeline; 2. System computer malfunction; 3. Vehicle speed sensor failure; 4. ABS wiring harness breakage. The ABS system consists of an ABS pump, wheel speed sensors, and a brake switch. Its working principle is: during emergency braking, the highly sensitive wheel speed sensors installed on each wheel detect wheel lock-up, and the computer controls the pressure regulator to release pressure from the wheel's brake cylinder to prevent wheel lock-up. The functions of the ABS system are: 1. To prevent vehicle loss of control, increase braking distance, and improve vehicle safety; 2. To improve the overall braking performance of the vehicle; 3. To prevent wheel lock-up during braking; 4. To ensure that the driver can control the direction during braking and prevent rear axle skidding.
Last time when my old car went for the annual inspection, the ABS light stayed on afterwards. It took me a while to figure out the reason. During the inspection, the mechanic needed to test the exhaust emissions, causing the front wheels to spin and slip on the rollers. The ABS sensor mistakenly thought the wheels were locked and triggered the warning light. Sometimes, careless inspectors forget to reconnect the ABS plug, or the sensors get covered in mud during undercarriage cleaning. However, the real concern should be actual malfunctions, such as the vibrations during inspection causing aged wheel speed sensor wiring to break completely. Later, I noticed the light remained on after starting the car, so I used an OBD scanner and found a fault code for the right front wheel. It turned out the plug was loose, and I fixed it by pressing it firmly back in place.
As a frequent visitor to repair shops, I've summarized three main reasons why the ABS light comes on after an inspection: First, hardware may be accidentally disturbed—the wiring harness of the wheel speed sensor under the car is easily scraped by testing equipment. Second, the system may not have been reset properly—some inspection stations disconnect the battery for testing, and the ABS computer needs to drive a few kilometers to recognize all components again. Third, it might reveal an actual issue, especially for older cars over five years old—those sensor connectors covered in grime can't withstand vibration. My advice is to drive a couple of kilometers first to see if the light turns off automatically. If it stays on, use a diagnostic tool to read the specific fault location. Don’t be like my neighbor who kept driving until the brakes started making strange noises before fixing it.
