What Causes the ABS Yellow Light to Illuminate in a Car?

[DelCali]

There are multiple 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 wheel 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 the wheel slip rate, thus failing to issue appropriate commands to adjust 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: Poor signal due to loose connections between system wires or poor contact of the ABS relay, leading to system failure. Solution: Check the wire 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 and 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, and examine the power supply (e.g., voltage relay or poor power contact). State 3: ABS warning light stays on after engine start and turns off only when the engine is turned off (IGFF). Cause: Poor grounding contact of the ABS hydraulic valve body; poor contact in the ABS hydraulic valve body's wire 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 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 recommended 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, preventing the driver from slowing down or adjusting the vehicle's trajectory, posing significant safety risks.

[OLeila]

The ABS light turns on yellow, and I've encountered it a few times. The most common cause is a faulty wheel speed sensor. Those sensors are located near the wheels and are prone to dust buildup or water ingress causing short circuits, leading to false alarms from the system. Another possibility is an issue with the ABS module itself or aging wiring harnesses causing poor contact—I once had to fix it due to a loose connector. Blown fuses in the circuit are also common; they trip when the current exceeds the limit, so it's worth checking the fuse box. Unstable battery voltage can also trigger it, especially during cold starts when voltage fluctuates. When this light is on, it means the anti-lock braking function isn't working, making it easy for the wheels to lock up and skid during hard braking, which is quite dangerous. I recommend going to a professional shop immediately to scan for trouble codes with a diagnostic tool—don't delay. Also, when washing your car, pay attention to cleaning the wheel sensor areas to prevent minor issues.