What causes the ABS light to come on in a Great Wall M4?

[StKhloe]

There are multiple conditions for the ABS light being on, with different causes and solutions for each condition, as detailed below: Condition 1: ABS warning light stays on (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 control unit from determining the vehicle speed and calculating the wheel slip rate, thereby failing to issue appropriate commands to regulate braking. Solution: Clean the contaminants from the wheel speed sensor and adjust the gap between the sensor and the tone 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 malfunction. Solution: Check all wiring connections and reconnect any loose parts. Condition 2: ABS warning light intermittently comes on but turns off when accelerating. Cause: When multiple electrical devices are in use, the battery voltage drops below 10.5V. The ABS warning light turns off as the engine speed increases and voltage rises. This may also occur due to insufficient power supply voltage to the ABS system, such as 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). Condition 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 wiring connector; ABS control unit malfunction. Solution: Loosen and then retighten the grounding screw on the hydraulic valve body, cleaning the contact surface if necessary; check for enlarged connector gaps; replace the ABS or ABS/ASR control unit. Condition 4: ABS warning light comes on during high-speed driving. Cause: At high speeds, the ABS control unit 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. Condition 5: ABS warning light intermittently comes on. 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 use a finger to push the brake switch linkage fully downward, then release the brake pedal to complete the self-setting position; replace the brake light switch if necessary. If the ABS warning light is on, it is advised 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, making it difficult for the driver to slow down or adjust the vehicle's trajectory, posing significant safety risks.

[DelMargaret]

I previously drove a Great Wall M4, and the ABS light suddenly coming on is indeed quite common. The most likely reason is that the wheel speed sensor is covered with dust or mud, especially during rainy days or when the road is dirty in winter. Additionally, if the brake fluid level is too low, the system will detect an abnormality and the light will come on. It could also be caused by loose wiring connections or uneven tire pressure leading to inconsistent wheel speeds, which often happens during stop-and-go city driving or after frequent hard braking. Once the ABS light is on, the anti-lock braking function may fail, making it very dangerous during emergency braking as the wheels could lock up and skid. Therefore, I recommend driving to a 4S shop as soon as possible for a professional inspection and using a diagnostic tool to check the fault codes. When driving normally, pay attention to keeping the sensors around the wheels clean to minimize issues and prevent small problems from turning into major ones. Safety first, after all.