What does it mean when the ABS light comes on when starting the car?

[LeStephen]

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 mud, sludge, or other contaminants, affecting its ability to detect the corresponding wheel speed signal. This prevents the ABS control unit from determining the vehicle speed and 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 tone ring to restore normal function. Cause 2: Poor signal due to loose connections between system wires or poor contact in the ABS relay, leading to system failure. Solution: Check wire connections and reconnect any loose parts. Condition 2: ABS warning light intermittently comes on but turns off when accelerating. Cause: When multiple vehicle 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. The ABS system 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 examine the power supply (e.g., voltage relay or poor power contact). Condition 3: ABS warning light stays on after engine start until 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 failure. Solution: Loosen and retighten the hydraulic valve body grounding screw, cleaning the contact surface if necessary; check if the connector gap has widened; replace the ABS or ABS/ASR control unit. Condition 4: ABS warning light comes on during high-speed driving. Cause: During high-speed driving, the ABS control unit detects a significant difference 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 push the brake switch linkage down fully with your fingers, then release the brake pedal to complete self-positioning; replace the brake light switch if necessary. If the ABS warning light is on, it is recommended not to continue driving. The illuminated ABS light indicates a fault 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.