What Causes the ABS Light to Illuminate?

[DeAbel]

There are various 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 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 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 between system wires or poor contact of the ABS relay, leading to system failure. Solution: Check the wire connections and reconnect any loose ones. 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, the voltage rises, and the ABS indicator 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; examine the power supply (e.g., voltage relay or poor power contact). State 3: ABS warning light remains on after engine start until the engine is turned off (IGFF). Cause: Poor grounding contact of the ABS hydraulic valve body; poor contact of the ABS hydraulic valve body wire connector; ABS computer malfunction. Solution: Loosen the grounding screw of the hydraulic valve body, then retighten it, cleaning the contact surface if necessary; check if the connector gap has widened; replace the ABS or ABS/ASR computer. 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. 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 of 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 the self-setting position; replace the brake light switch. If the ABS warning light is on, it is advisable not to continue driving. An illuminated ABS light 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 slowing down or adjusting the vehicle's trajectory, posing significant safety risks.

[Philip]

I remember driving for over ten years, and the ABS light has come on several times, mainly due to minor faults in the anti-lock braking system. The most common situation is when the sensors on the wheels get clogged with mud or metal debris, blocking signal transmission and causing the ABS warning light to illuminate. Additionally, loose or aged wiring connections, issues with the ABS control module, or low battery voltage can also trigger the light. Once, my car's light came on after a heavy rainstorm, and it turned out to be caused by muddy water splashing into the sensor. I recommend that car owners first check for dirt around the wheels. If you're not confident in your DIY skills, it's best to visit a professional repair shop as soon as possible. After all, if the ABS fails, braking on slippery roads can lead to skidding, posing significant safety risks. Regularly cleaning the undercarriage components during car washes can prevent many issues. Maintaining a properly functioning braking system is crucial—don't wait for an accident to happen before regretting it.