What does it mean when the ABS warning light comes on in a vehicle?

[McGiselle]

When a car displays ABS, 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, preventing the driver from slowing down or adjusting the vehicle's trajectory, which poses significant safety risks. There are several states in which the ABS light may illuminate, each with different causes and solutions, as detailed below: State 1: ABS warning light stays on continuously (most common). Cause 1: The ABS 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's speed and the wheel 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 speed sensor and the signal ring to restore normal function. Cause 2: Poor signal transmission due to loose connections between system wires or poor contact in 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 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 warning 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 stays 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's wire connector; ABS computer malfunction. Solution: Loosen and then retighten the grounding screw on 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, push the brake switch linkage down fully with your finger, then release the brake pedal to complete the self-setting position; replace the brake light switch if necessary.