What Causes the ABS Light to Illuminate When Starting the Car?

[Rose]

There are various states in which the ABS light may illuminate, with different causes and solutions for each state, as detailed below: State 1: ABS warning light remains constantly on (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 computer from determining the vehicle speed and 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 in the system wiring or poor contact in the ABS relay, leading to system malfunction. Solution: Check all wiring 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 light 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 on after engine start and only turns off when the engine is turned off (IGFF). Cause: Poor grounding contact in the ABS hydraulic valve body; poor contact in the ABS hydraulic valve body wiring connector; ABS computer malfunction. Solution: Loosen and retighten the hydraulic valve body's grounding screw, 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: At high speeds, 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, typically listed on the fuel tank cap sticker. 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, manually push the brake switch linkage down fully, then release the pedal to reset its position; replace the brake light switch if necessary. If the ABS warning light is on, 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 path, posing significant safety risks.