Why is the ABS light always on?
4 Answers
There are various states of the ABS light being on, with different causes and solutions for each state. 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's speed and the wheel's slip rate, thus failing to issue appropriate commands to adjust 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 and the voltage rises, the ABS indicator light turns off. The ABS system's 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 grounding contact in the ABS hydraulic valve body; poor contact in the ABS hydraulic valve body's wiring connector; ABS computer malfunction. Solution: Loosen and then retighten the grounding screw on the hydraulic valve body, 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: 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 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, as it 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.
I encountered this situation the last time I drove too! The ABS light staying on is really unsettling. The most common issue is a dirty or faulty wheel speed sensor—these are located right next to the wheels and are prone to getting covered in mud or damaged by small stones. Another possibility is a loose connection in the brake system wiring, especially problematic during rainy weather. I suggest you quickly check the circular metal sensor rings on all four wheels to see if they’re clogged with too much metal debris. Oh, and whatever you do, don’t pull the ABS fuse and keep driving—it can make braking unreliable. My friend almost rear-ended someone on the highway last time because of that. The safest bet is to take it to a reliable repair shop and have them scan for trouble codes with a diagnostic tool—they can pinpoint exactly which wheel is causing the issue in just a few minutes.
A constantly illuminated ABS light is no trivial matter. Just yesterday, I helped my neighbor check his old car and found it was caused by water seepage in the left front wheel sensor connector. Additionally, this light may also indicate low brake fluid or the use of substandard brake fluid—excessive air bubbles in the fluid can interfere with signal transmission. Another less common reason: have you replaced the tires with mismatched sizes? Significant differences in tread depth can confuse the ABS computer. My car had this light on for a whole week last time because of this issue, and it disappeared immediately after replacing all four tires. If the wiring harness gets shaken loose when going over potholes, it's even more troublesome—repairs are labor-intensive and costly. It's better to identify the root cause early.
The light being on indicates the anti-lock braking system has failed. Focus on checking those small black nodules on the inner side of each tire—the wheel speed sensors. I've personally seen mechanics replace these during repairs; it's quite labor-intensive requiring wheel and liner removal. Additionally, burnt-out relays in the ABS main pump are common, especially in flood-damaged vehicles. Here's a money-saving tip: try restarting the engine three times first—sometimes false alarms can self-cancel. If that doesn't work, perform a self-test: find an open area and stomp the brakes hard. If you hear a clattering vibration sound, it means the pump still functions, but for safety's sake, checking the trouble codes would be more reassuring.
