What causes the ABS light to come on after vehicle inspection?

[Margaret]

There are multiple states of the ABS warning light, 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, dirt, or other contaminants, affecting its ability to detect the corresponding speed signal. This prevents the ABS control module 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 signal ring to restore normal function. Cause 2: Loose connections between system wiring or poor contact in ABS relays causing signal issues and system failure. Solution: Check wiring connections and reconnect any loose parts. State 2: ABS warning light comes on intermittently, turning off during acceleration. Cause: When multiple vehicle electrical devices are in use, the battery voltage drops below 10.5V. The ABS warning light turns off as 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). State 3: ABS warning light stays on after engine start until the engine is turned off. Cause: Poor grounding contact in the ABS hydraulic valve body; poor electrical connector contact in the ABS hydraulic valve body; ABS control module failure. Solution: Loosen and then retighten the grounding screw on the hydraulic valve body, cleaning the contact surface if necessary; check for increased gap in connectors; replace the ABS or ABS/ASR control module. State 4: ABS warning light comes on during high-speed driving. Cause: During high-speed driving, the ABS control module detects a significant difference between rear and front wheel speeds; 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 comes on intermittently. 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 all the way down, 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 advisable 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.