What does it mean when the ABS anti-lock braking system warning light comes on?

[VanReid]

When a car displays ABS, it indicates a malfunction in the vehicle's anti-lock braking system. During emergency braking, if the wheels lock up, the vehicle may lose control and skid, preventing the driver from decelerating 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 part 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's slip rate, thus failing to issue appropriate commands to adjust 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: Loose connections between system wires or poor contact in the ABS relay can cause signal issues, leading to system failure. Solution: Check 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, the voltage rises, and 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 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, loose wiring connections in the ABS hydraulic valve body, or ABS computer malfunction. Solution: Loosen and retighten the grounding screws on the hydraulic valve body, clean contact surfaces if necessary, check for enlarged gaps in connectors, and replace the ABS or ABS/ASR computer if needed. State 4: ABS warning light illuminates during high-speed driving. Cause: During high-speed driving, the ABS computer detects a significant discrepancy between rear and front wheel speed signals, or incorrect tire or wheel rim specifications. Solution: Refer to the vehicle's tire and wheel rim specifications, as indicated on the fuel tank cap label. State 5: ABS warning light intermittently illuminates. Cause: Improper adjustment of the brake light switch or internal poor contact in the brake light. Solution: With the engine running, press the brake pedal, push the brake switch linkage down fully with a finger, then release the brake pedal to complete self-positioning. Replace the brake light switch if necessary.