What causes the ABS light to illuminate on a car?

[LondonFitz]

There are various states of the ABS light being illuminated, with different causes and solutions for each state, as detailed below: State 1: ABS warning light stays on continuously (most common). Cause 1: The ABS 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 regulate 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 transmission due to loose connections between system wires or poor contact in 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 during acceleration. 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'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 remains 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 electrical connection in the ABS hydraulic valve body; 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. 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 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, preventing the driver from slowing down or adjusting the vehicle's trajectory, posing significant safety risks.

[Donna]

Oh no, the ABS light coming on is really unsettling. I remember one time my car had this issue - ABS stands for Anti-lock Braking System, and the light indicates the system's self-check failed. There could be several reasons: maybe the wheel sensors are dirty or damaged (especially after driving on muddy roads where sensors get covered in sludge). Poor wiring connections, short circuits, or broken wires might also trigger the light. ABS control module failure or blown fuses are more serious issues requiring professional repair. Low battery voltage can sometimes affect its operation too. While regular braking still works when the ABS light is on, emergency stops may cause wheel lock-up and skidding, increasing accident risks. I recommend getting it checked at a repair shop ASAP - don't procrastinate like I did initially, since safety comes first. Regularly cleaning wheel sensors can help prevent such issues.

[McHarper]

I'm someone who enjoys tinkering with automotive electronic systems, and I've encountered the ABS light issue before. The anti-lock braking system relies on wheel speed sensor data, and if the sensor malfunctions—such as aging damage or water corrosion—the light may stay on or flicker. Wiring problems are common, like loose connectors or worn wires causing short circuits or open circuits, preventing signals from reaching the control module properly. A faulty ABS module or a blown fuse can also trigger this. During inspection, you can use an OBD diagnostic tool to read fault codes and quickly pinpoint the issue. Repairs can be costly, with a new module costing several hundred, while cleaning or replacing a sensor is much simpler. Ignoring it may lead to system failure, significantly increasing the risk of losing control during emergency braking on slippery roads, so addressing it promptly is wise.

[MacNathan]

The ABS light is a warning signal that should never be ignored. The ABS system prevents wheel lock-up, and when the light is on, it means the wheels may lock and skid during emergency braking, significantly increasing the risk of skidding or rollover, which is extremely dangerous. Common triggers include sensor malfunctions, control module errors, or wiring breaks, with blown fuses also being a potential cause. Unstable battery voltage can also trigger the light. If this happens, immediately slow down, pull over, and check for safety. Delaying repairs is equivalent to voluntarily giving up an important protective function, posing a major threat to driving safety. I recommend developing the habit of keeping sensors clean to avoid dirt buildup and checking brake fluid levels every three months to effectively prevent the light from coming on.