Why does the ABS light stay on after vehicle inspection?

[OKaden]

When a car displays the ABS light, it indicates a malfunction in the vehicle's Anti-lock Braking System. During emergency braking, if the wheels lock up, the vehicle may skid uncontrollably, preventing the driver from decelerating or adjusting the vehicle's trajectory, which poses significant safety hazards. There are various states of the ABS light being on, with different causes and solutions for each state, as detailed below: State 1: ABS warning light stays on continuously (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 speed and the wheel 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: 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 turns on, 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 indicator light turns off. This can 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 electrical connector; 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's gap has widened; replace the ABS or ABS/ASR computer. State 4: ABS warning light turns on 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 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: With the engine running, depress 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.