What Causes the ABS Light to Illuminate During Vehicle Inspection?
2 Answers
ABS light illumination can occur in various states, each with different fault causes and corresponding solutions, as detailed below: State 1: ABS warning light remains constantly illuminated (most common). Cause 1: The ABS wheel speed sensor's sensing area is covered by dirt, mud, or other contaminants, affecting its ability to detect the corresponding speed signal. This prevents the ABS control unit from determining the vehicle speed and wheel slip rate, thus failing to issue appropriate commands to regulate braking. Solution: Clean the contaminants from the wheel speed sensor and adjust the gap between the sensor and the tone ring to restore normal function. Cause 2: Poor signal transmission due to loose connections in the system wiring or faulty ABS relay contacts, leading to system malfunction. Solution: Inspect wiring connections and reconnect any loose terminals. State 2: ABS warning light intermittently illuminates but turns off during acceleration. Cause: When multiple electrical devices are in use, the battery voltage drops below 10.5V. As engine speed increases and voltage rises, the ABS light turns off. This may also occur due to insufficient power supply voltage to the ABS system, such as poor terminal contact or grounding issues. Solution: Check the battery's specific gravity, inspect the charging system, and verify the power supply (e.g., voltage relay or poor power contact). State 3: ABS warning light remains illuminated after engine start and only turns off when the engine is turned off (IGFF). Cause: Poor grounding contact in the ABS hydraulic valve body, faulty wiring connections in the valve body, or ABS control unit failure. Solution: Loosen and retighten the grounding screw of the hydraulic valve body, cleaning the contact surface if necessary. Check for enlarged terminal gaps and replace the ABS or ABS/ASR control unit if required. State 4: ABS warning light illuminates during high-speed driving. Cause: The ABS control unit detects a significant discrepancy between rear and front wheel speed signals during high-speed driving, or incorrect tire/wheel specifications. Solution: Refer to the vehicle's specified tire and wheel dimensions, typically listed on the fuel cap label. State 5: ABS warning light intermittently illuminates. Cause: Improper adjustment of the brake light switch or internal contact issues in the brake lights. Solution: With the engine running, press the brake pedal and manually push the brake switch lever fully downward, then release the pedal to reset its position. Replace the brake light switch if necessary. If the ABS warning light is illuminated, it is advised not to continue driving. ABS failure means the anti-lock braking system is compromised, potentially causing wheel lock-up during emergency braking. This may result in loss of vehicle control, skidding, and inability to decelerate or adjust trajectory, posing significant safety risks.
It's quite common for the ABS light to come on during vehicle inspection, especially after the annual inspection equipment accesses the OBD system, which may mistakenly trigger fault codes. There are several main reasons: dust or iron filings accumulated on the wheel speed sensor, interfering with signal transmission; loose or vibrating wiring connectors; or possibly an issue with the ABS control module, though this is less likely. Once, when I was helping a friend check their car, cleaning the sensors fixed the problem. I suggest you try turning the car off and restarting it after the inspection. If the light is still on, prioritize cleaning the mud around the sensors—just gently brush the wheel hub with a soft brush. If that doesn’t work, read the fault code to confirm the source and take it to a professional repair shop without delay. ABS failure can affect the anti-lock braking function, so be extra careful when driving in the rainy season.
