What does it mean when the ABS yellow light on the dashboard is on?

[KevinRose]

When the ABS light is displayed on the car, 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, making it difficult for the driver to slow down or adjust the vehicle's trajectory, which poses a significant safety hazard. There are several states in which the ABS light may illuminate, with different causes and solutions for each state, as detailed below: State 1: ABS warning light stays on (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 or 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: Poor signal due to loose connections in the system wiring or poor contact in the ABS relay, leading to system failure. Solution: Check the wiring 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 drops below 10.5V. As the engine speed increases and the voltage rises, the ABS light turns off. The ABS system's power supply voltage is too low, possibly due to poor terminal contact or grounding issues. Solution: Check the battery's specific gravity, inspect the charging system, and verify 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; ABS computer malfunction. Solution: Loosen and then retighten the grounding screw of the hydraulic valve body, cleaning the contact surface if necessary. Check if the connector gap has widened; 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 the rear and front wheel speed signals. Incorrect tire or wheel rim specifications may also be the cause. 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: Start the engine, press the brake pedal, and push the brake switch linkage down with a finger to its limit. Then release the brake pedal to complete the self-setting position. Replace the brake light switch if necessary.