Why is the ABS light always on?
2 Answers
When the car displays ABS, it means there is a malfunction in the vehicle's Anti-lock Braking System. During emergency braking, if the wheels lock up, the vehicle may lose control and skid, preventing the driver from slowing down or adjusting the vehicle's trajectory, which poses significant safety risks. The ABS light can illuminate in various states, each with different causes and solutions. The details are as follows: State 1: ABS warning light stays on (most common). Cause 1: The ABS speed sensor's sensing part 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 wheel slip rate, thus failing to issue appropriate commands to regulate 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 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 turns on 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 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 stays on after engine start and only turns off when the engine is turned off (IGFF). Cause: Poor contact in the ABS hydraulic valve body's grounding circuit; poor contact in the ABS hydraulic valve body's wiring 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 turns on 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 turns on. Cause: Improper adjustment of the brake light switch; poor internal contact in the brake light. Solution: Start the engine, press the brake pedal, push the brake switch linkage down with your finger, then release the brake pedal to complete the self-setting position; replace the brake light switch if necessary.
I'm a female owner driving an older Ford Focus, and last month the ABS light came on too. When I took it to the repair shop, they found that the left front wheel speed sensor was covered in mud. It was fine after being cleaned during a car wash. If the sensor was really broken, replacing it wouldn’t be expensive—just around a hundred bucks. But sometimes the issue is more complicated, like uneven brake disc wear causing abnormal data, or a loose wiring connector in the ABS pump. I suggest going to an auto repair shop first to read the trouble codes. Don’t be like my friend who ignored the light for half a year and only regretted it when the brake pedal shook violently during braking.
