Why does the ABS light come on after a vehicle inspection?
2 Answers
When the car displays an ABS light, it indicates a malfunction in the vehicle's Anti-lock Braking System. If the wheels lock up during emergency braking, the vehicle may lose control and skid, making it difficult for the driver to slow down or adjust the vehicle's trajectory, which poses a significant safety hazard. There are several states in which the ABS light may illuminate, each with different causes and solutions, as detailed below: State 1: The ABS warning light remains constantly on (most common). Cause 1: The ABS 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 computer from determining the vehicle's speed and the wheel's slip rate, thus failing to issue appropriate commands to regulate braking. Solution: Clean the dirt from the speed sensor and adjust the gap between the sensor and the signal ring to restore normal function. Cause 2: Loose connections between system wires or poor contact in the ABS relay can lead to signal issues, causing system failure. Solution: Check the wire connections and reconnect any loose parts. State 2: The ABS warning light intermittently comes on and turns off when accelerating. Cause: When multiple vehicle electrical devices are in use, the battery voltage may drop below 10.5V. As the engine speed increases and voltage rises, the ABS light turns off. This can also occur if the ABS system's power supply voltage is too low due to poor wire contact or grounding issues. Solution: Check the battery's specific gravity, inspect the charging system, and examine the power supply (e.g., voltage relay or poor power contact). State 3: The ABS warning light stays on after the engine starts and only turns off when the engine is turned off (IGFF). Cause: Poor grounding contact in the ABS hydraulic valve body, loose wiring connections in the ABS hydraulic valve body, or a faulty ABS computer. Solution: Loosen and then retighten the grounding screw on the hydraulic valve body, cleaning the contact surface if necessary. Check for enlarged gaps in the connectors and replace the ABS or ABS/ASR computer if needed. State 4: The ABS warning light comes on during high-speed driving. Cause: At high speeds, the ABS computer detects a significant discrepancy between the rear and front wheel speed signals. This can also occur if the tire or wheel rim specifications are incorrect. Solution: Refer to the vehicle's tire and wheel rim specifications, as indicated on the label near the fuel tank cap. State 5: The ABS warning light intermittently illuminates. Cause: Improper adjustment of the brake light switch or poor internal contact in the brake light. Solution: Start the engine, press the brake pedal, and use a finger to push the brake switch linkage all the way down. Release the brake pedal to complete the self-setting position. Replace the brake light switch if necessary.
I just had my car inspected and the ABS light came on. I've seen this situation many times. Most of the time, it's because during the inspection they test the brake system, and the vibration causes the wheel speed sensor to loosen or get dirty. When dust accumulates on the sensor, the signal can't transmit properly. The ABS system prevents wheel lock-up during emergency braking to avoid skidding. If the light comes on, it means the protective function has failed. Driving like this is especially dangerous in rainy conditions when the road is slippery and you can't brake effectively. Last year, my old car had the same issue after inspection. I drove it to my friend's shop to check, and the computer diagnosis showed a fault in the left front wheel speed sensor. After cleaning the connection, the light went off. Remember, don't delay—get it checked by a professional as soon as possible. It saves money, hassle, and ensures safety. For prevention, just wipe around the wheel speed sensor area every time you wash your car to reduce dust buildup.
