What Causes the ABS Light on the Car Dashboard to Illuminate?

[DeArthur]

There are multiple 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 constantly (most common). Cause 1: The ABS wheel speed sensor's sensing area is covered by mud, sludge, 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, thereby 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 transmission 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, the voltage rises, causing the ABS light to turn off. This may 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, and examine the power supply (e.g., voltage relay or poor power contact). State 3: ABS warning light remains on after engine start and only turns off when the engine is turned off (IGFF). Cause: Poor grounding connection in the ABS hydraulic valve body; loose wiring connector in the ABS hydraulic valve body; ABS computer malfunction. Solution: Loosen and retighten the grounding screw on the hydraulic valve body, cleaning the contact surface if necessary. Check for enlarged gaps in the connector. Replace the ABS or ABS/ASR computer if needed. State 4: ABS warning light illuminates during high-speed driving. Cause: At high speeds, the ABS computer detects a significant discrepancy between the rear and front wheel speed signals. This may also occur due to 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 in the brake light. Solution: With the engine running, press the brake pedal and manually push the brake switch lever down completely. Release the brake pedal to complete the self-setting process. Replace the brake light switch if necessary. If the ABS warning light is on, it is recommended not to continue driving, as this 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.

[DiCamilla]

I've driven many cars and done my own repairs. When the ABS light comes on, it's usually due to an issue with the wheel speed sensor. The sensor is located on the hub and can get dirty with mud or sand, or the connector may become loose, causing inaccurate detection. It could also be a faulty ABS control module that needs replacement, or a broken wire causing poor contact. Additionally, insufficient brake fluid or a blown fuse can trigger the warning light. Once the ABS light is on, the anti-lock braking function may be disabled. When driving, avoid sharp turns or sudden braking to prevent skidding. It's recommended to first check and clean the sensors near the tires. If that doesn't work, take it to a professional repair shop to scan for fault codes with a computer—don't delay as safety comes first. This issue is quite common; I've seen it many times. Regular maintenance can reduce the chances of it happening and ensure stable, worry-free driving.