What Causes the ABS and Exclamation Mark Lights to Illuminate?
3 Answers
ABS light can illuminate in various states, 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 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 wheel slip rate, thus failing to issue appropriate commands to regulate braking. Solution: Clean the contaminants 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 malfunction. Solution: Check wire 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 voltage rises, the ABS light turns off. This can 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, 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 wire connector; ABS computer malfunction. Solution: Loosen and 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. 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. 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: 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 self-positioning; replace the brake light switch if necessary. If the ABS warning light is on, it is advised 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 path, posing significant safety risks.
Recently, both the ABS light and the exclamation mark light on my dashboard came on, which made me quite nervous while driving. It happened after I drove in heavy rain and felt the brakes were a bit soft. The next day, these warning lights appeared on the dashboard. I pulled over to check the handbrake first and confirmed it was fully released. Then, I opened the hood to inspect the brake fluid reservoir and noticed the fluid level was just above the MIN line, suggesting a possible leak or seepage. At the repair shop, the mechanic said it might be due to mud clogging the wheel speed sensors or a minor fault in the brake system circuit. If left unrepaired, the ABS wouldn't function, increasing the risk of wheel lock-up during braking, especially on wet or slippery roads. After spending half a day cleaning the sensors, the lights went off, and everything was fine. I recommend friends regularly check their brake fluid to prevent potential issues.
It's quite common for the ABS light and exclamation mark light to illuminate simultaneously, often caused by a faulty wheel speed sensor or insufficient brake fluid. When the sensor is covered in dust or the connector ages, unstable signals trigger the ABS warning. Low brake fluid directly causes the exclamation mark light to come on. In such cases, prioritize checking the brake fluid level—it should be between the upper and lower marks on the reservoir. If that's fine, it might be a circuit short or worn brake pads. Don't ignore it; ABS failure reduces braking stability, posing significant risks at high speeds. Visit a professional shop promptly to diagnose the trouble codes with a scanner, ensuring peace of mind after repairs.
