What causes the ABS light to illuminate in a car?
2 Answers
ABS light illumination can occur in various states, with different causes and solutions for each state. The details are as follows: State 1: ABS warning light remains constantly lit (most common). Cause 1: The ABS wheel speed sensor's sensing area is covered by dirt, mud, or other contaminants, affecting the sensor's ability to detect the corresponding speed signal. This prevents the ABS computer from determining the vehicle speed and calculating the wheel slip rate, thus failing to issue appropriate commands to regulate braking. Solution: Clean the dirt from the wheel speed sensor and adjust the gap between the sensor and the signal ring to restore normal function. Cause 2: Poor signal transmission due to loose connections between system wires or poor contact of the ABS relay, leading to system failure. Solution: Inspect wire connections and reconnect any loose parts. State 2: ABS warning light intermittently illuminates but turns off during acceleration. Cause: When multiple vehicle electrical devices are in use, the battery voltage drops below 10.5V. As the engine speed increases and voltage rises, the ABS indicator turns off. This may also occur if the ABS system's power supply voltage is too low due to poor terminal contact or grounding issues. Solution: Check the battery's specific gravity; inspect the charging system; examine the power supply (e.g., voltage relay or poor power contact). State 3: ABS warning light remains lit after engine start and only turns off when the engine is turned off (IGFF). Cause: Poor grounding contact of the ABS hydraulic valve body; poor contact in the ABS hydraulic valve body's wire connector; ABS computer malfunction. Solution: Loosen and then retighten the grounding screw of the hydraulic valve body, cleaning the contact surface if necessary; check if the connector gap has widened; replace the ABS or ABS/ASR computer. State 4: ABS warning light illuminates during high-speed driving. Cause: During high-speed driving, the ABS computer detects a significant discrepancy between the rear and front wheel speed signals; incorrect tire or wheel rim specifications. Solution: Refer to the vehicle's tire and wheel rim specifications, as indicated on the label near the fuel tank cap. State 5: ABS warning light intermittently illuminates. Cause: Improper adjustment of the brake light switch; poor internal contact in the brake light. Solution: With the engine running, press the brake pedal and use a finger to push the brake switch linkage fully downward, then release the brake pedal to complete the self-setting position; replace the brake light switch if necessary. If the ABS warning light is illuminated, it is advised not to continue driving. An illuminated ABS light indicates a malfunction in the vehicle's anti-lock braking system. During emergency braking, if the wheels lock up, the vehicle may skid uncontrollably, preventing the driver from slowing down or adjusting the vehicle's trajectory, posing significant safety risks.
When I first learned to drive, the ABS light came on, which scared me. It means there might be a problem with the anti-lock braking system. A common cause is that the wheel speed sensor is dirty or damaged, or too much dust or mud has accumulated near the wheel, blocking the sensor. Another possibility is a blown fuse, which can easily break the circuit with just a light touch. Although the light is on, the normal brakes still work, but you lose the anti-lock protection during emergency braking, making it easy to skid or even lose control on wet or slippery roads. The last time I encountered this was while driving on the highway in the rain—I almost rear-ended someone, which was really close. It's best to go to a professional repair shop as soon as possible. The technician can use a diagnostic tool to scan and identify the specific issue before it worsens. Also, when washing your car, regularly clean the mud and dirt inside the wheels to prevent sensor problems and stay safe.
