What Causes the ABS Light to Illuminate While Driving?

[OJustin]

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 sensing part of the ABS speed sensor 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 or the wheel 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 between system lines or poor contact of the ABS relay, leading to system failure. Solution: Check the line connections and reconnect any loose parts. State 2: ABS warning light intermittently illuminates 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, and 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 of the ABS hydraulic valve body; poor contact of the ABS hydraulic valve body wiring connector; ABS computer malfunction. Solution: Loosen and then retighten the grounding screw of the hydraulic valve body, cleaning the contact surface if necessary. Check if the connector gap has widened. Replace the ABS or ABS/ASR computer if needed. State 4: ABS warning light illuminates 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 may also be a factor. 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 illuminates. Cause: Improper adjustment of the brake light switch; poor internal contact of the brake light. Solution: Start the engine, press the brake pedal, and push the brake switch linkage down with your finger to its limit. 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. 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.

[VonOwen]

I've been driving for over a decade and have encountered the ABS light coming on a few times. The first time I noticed the light, I panicked. Later, after some research, I figured it might be due to a dirty or faulty sensor, especially when driving on rough roads in rainy or snowy weather where mud, gravel, and debris can clog the sensor and prevent it from sending signals. Another common issue is wiring problems—wear and tear, short circuits, or electrical faults—which cause the ABS computer to receive incorrect signals and trigger the warning light. Sometimes, the control module malfunctions, similar to a smartphone freezing, causing the system to fail its self-check. The simplest scenario could be a blown fuse, where a small component failure disrupts the entire circuit. The light coming on doesn’t mean the ABS fails immediately, but braking force can become unstable. I’ve experienced wheel lock-up and dangerous skidding during braking. So, whenever the ABS light comes on, I usually head straight to a reliable repair shop for a check-up to avoid bigger issues. Regularly cleaning around the wheels during car washes can help prevent some of these problems.