What are the causes of ABS system failure?
4 Answers
There are various conditions when the ABS light is on, and different conditions have different causes and solutions, as detailed below: Condition 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 and the wheel slip rate, thus failing to issue appropriate commands to regulate braking. Solution: Clean the dirt on 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. Condition 2: ABS warning light intermittently turns on and turns off when accelerating. Cause: When multiple vehicle electrical devices are in use, the battery voltage drops below 10.5V. The ABS warning light turns off as the engine speed increases and voltage rises. 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; examine the power supply (e.g., voltage relay or poor power contact). Condition 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 failure. 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. Condition 4: ABS warning light turns on during high-speed driving. Cause: During high-speed driving, the ABS computer detects a significant difference 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. Condition 5: ABS warning light intermittently turns on. Cause: Improper adjustment of the brake light switch; poor internal contact of the brake light. Solution: With the engine running, press the brake pedal and push the brake switch linkage down with your finger, then release the brake pedal to complete the self-setting position; replace the brake light switch. If the ABS warning light is on, it is recommended not to continue driving. An illuminated ABS light indicates a fault 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.
I was also really nervous last time my ABS light came on. ABS faults generally fall into three main categories: wheel speed sensors are the most common issue, where mud or metal shavings sticking to the probe can trigger false fault codes; problems with the ABS pump are more troublesome, as damage to the control unit or seized solenoid valves can cause the system to fail; the scariest issue is actually wiring degradation, like rodents chewing wires or loose connectors. I remember that time they diagnosed a faulty left rear wheel sensor, and replacing it cost me over 400 bucks. If the ABS fails, the brakes will shudder when pressed, so you must take it to a repair shop for a computer scan. Remember to avoid tire punctures or uneven wear affecting the sensors, and rinse the undercarriage thoroughly after driving through water.
Having repaired cars for over 20 years, I've seen too many ABS failures. In ordinary family cars, wheel speed sensors fail most frequently, often triggering warnings due to dirty magnetic rings after tens of thousands of kilometers. Next in line are hydraulic unit oil leaks or connector corrosion. Two years ago, an old BMW had ABS failure, and upon inspection, three wires in the engine bay harness were found chewed through by rats. Here's a money-saving tip: after ignition, observe whether the ABS light on the dashboard extinguishes within 6 seconds—if it stays lit, there's definitely a fault. A reminder: if ABS fails, don't slam on the brakes; the correct approach is to pump the brakes firmly and then release. Nowadays, new models come with stability control systems, making it even more dangerous when ABS fails, as it can cause ESP to malfunction as well.
As an owner with an electronics engineering background, I focus on the physical causes of ABS failures. The wheel speed sensors operate on electromagnetic induction principles and lose accuracy when the gap exceeds 0.5mm. The control module is particularly sensitive to voltage fluctuations, automatically shutting down when battery voltage drops below 9V. Experimental data shows a 78% error rate when sensors are contaminated with iron debris. Interestingly, 25% of vehicles report ABS faults after brake modifications, primarily due to altered reluctor ring spacing. When the ABS warning light stays on, the ECU automatically disables anti-lock functionality, increasing braking distance by 15-30%. These figures demonstrate the system's need for precise calibration.
