What does it mean when the ABS light is on in the car?

[EdwardLee]

When the car displays ABS, it means there is a fault in the vehicle's anti-lock braking system. During emergency braking, if the wheels lock up, the vehicle may lose control and skid, making it difficult for the driver to slow down or adjust the vehicle's trajectory, posing significant safety risks. There are multiple states in which the ABS light may illuminate, each with different causes and solutions, 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 the sensor's ability to detect the corresponding speed signal. This prevents the ABS computer from determining the vehicle's speed or the wheel's 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: Loose connections between system wires or poor contact in the ABS relay can lead to signal issues and system failure. Solution: Inspect wire connections and re-secure any loose ones. State 2: ABS warning light intermittently turns on 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 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: 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; loose wiring connections in the ABS hydraulic valve body; ABS computer malfunction. Solution: Loosen and then re-tighten the grounding screws on the hydraulic valve body, cleaning the contact surfaces if necessary. Check for widened gaps in the connectors. Replace the ABS or ABS/ASR computer if needed. State 4: ABS warning light turns on during high-speed driving. Cause: The ABS computer detects a significant discrepancy between rear and front wheel speed signals during high-speed driving. This may also occur due to incorrect tire or wheel rim specifications. Solution: Refer to the vehicle's tire and wheel rim specifications, typically found on the sticker near the fuel tank cap. State 5: ABS warning light intermittently turns on. Cause: Improper adjustment of the brake light switch; 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. Then release the brake pedal to complete the self-setting position. Replace the brake light switch if necessary.