What does it mean when the ABS light on the car stays on?

[JohnAnn]

The ABS light on the car indicates a malfunction in the vehicle's Anti-lock Braking System. During emergency braking, if the wheels lock up, the vehicle may skid uncontrollably, making it difficult for the driver to slow down or adjust the vehicle's trajectory, which poses a significant safety hazard. There are several scenarios where the ABS light may illuminate, each with different causes and solutions: Scenario 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 its ability to detect the vehicle's speed signal. This prevents the ABS computer from determining the speed and calculating the wheel slip rate, thus failing to issue commands to adjust braking. Solution: Clean the dirt from the speed sensor and adjust the gap between the sensor and the signal ring to restore normal function. Cause 2: Loose connections in the system wiring or poor contact in the ABS relay lead to signal issues, causing system failure. Solution: Check the wiring connections and reconnect any loose parts. Scenario 2: ABS warning light intermittently illuminates and turns off when accelerating. Cause: When multiple 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. Low system voltage due to poor wire connections or grounding issues can also cause this. Solution: Check the battery's specific gravity, inspect the charging system, and verify the power supply (e.g., voltage relay or poor power connections). Scenario 3: ABS warning light stays on after engine start and only turns off when the engine is turned off (IGFF). Cause: Poor grounding of the ABS hydraulic valve body, loose wiring connections in the 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 widened connector gaps, and replace the ABS or ABS/ASR computer if needed. Scenario 4: ABS warning light illuminates during high-speed driving. Cause: The ABS computer detects a significant discrepancy between rear and front wheel speeds during high-speed driving, 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. Scenario 5: ABS warning light intermittently illuminates. Cause: Improper adjustment of the brake light switch or poor internal contact in the brake light. Solution: Start the engine, press the brake pedal, manually push the brake switch lever down fully, then release the pedal to reset its position. Replace the brake light switch if necessary.