Why is the ABS yellow light on in a sedan?
2 Answers
When a car displays the ABS light, it indicates 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 decelerating 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, as detailed below: State 1: ABS warning light stays on (most common). Cause 1: The ABS wheel speed sensor's sensing area 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's 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 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 illuminates but turns off during acceleration. 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 turns off. This may also occur if the ABS system's power supply voltage is too low, such as 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 illuminates during high-speed driving. Cause: At high speeds, 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 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, push the brake switch linkage down fully with a finger, then release the brake pedal to complete the self-setting position; replace the brake light switch if necessary.
Having worked in car repairs for so many years, I've seen quite a few cases where the ABS light turns yellow, and there are many possible causes. The wheel speed sensor is the most common point of failure—dust, water stains, or oil contamination can disrupt the signal, especially after rain or driving through water. Aging or damaged wiring harnesses can also cause short circuits or open circuits, and ABS control module failures are not uncommon either, such as burnt internal circuit boards. Once the light comes on, the anti-lock braking system basically stops working, causing the tires to lock up during emergency braking, increasing the risk of losing control or skidding, especially on slippery roads. I recommend that car owners first check the ABS-related fuses in the fuse box to see if they’ve blown and try replacing them with new ones. If that doesn’t work, take the car to a proper repair shop immediately to read the fault codes with a diagnostic tool—don’t delay, as safety is no small matter. Regularly cleaning the sensors and inspecting the wiring harness can effectively prevent these issues.
