The ABS light comes on when the anti-lock brake system finds a fault and switches itself off. Your normal brakes still work, but the wheels can lock under hard braking. Traction control and stability control use the same wheel speed sensors, so the traction control light usually comes on at the same time. The most common cause is a failed wheel speed sensor or damaged sensor wiring.
ABS light vs brake warning light
| Light | Meaning | What to do |
|---|---|---|
| Amber ABS light | Anti-lock function disabled; normal braking still works | Drive carefully, leave extra stopping distance, and diagnose soon |
| Traction or stability light, steady | System disabled, often because of the same ABS fault | Same as above; take extra care on wet or icy roads |
| Traction light flashing while driving | System actively working because a wheel is slipping | Normal; ease off the throttle |
| Red brake warning light | Low brake fluid, a hydraulic problem, or the parking brake is on | Check the parking brake and fluid; do not drive if braking feels wrong |
Common causes of an ABS light
- Wheel speed sensor failure: the most common cause; see wheel speed sensor.
- Damaged wiring at a wheel, where the harness flexes with the suspension.
- Cracked or rusted tone ring that the sensor reads.
- Low brake fluid, which turns on warning lights on some vehicles.
- Blown ABS fuse or low battery voltage after a jump-start; see bad alternator symptoms.
- ABS module or pump failure, less common and more expensive.
How to diagnose it
- Use a scan tool that reads the ABS module; basic engine code readers only show engine codes, while ABS faults are stored as C-codes in the brake module.
- Check brake fluid level and the ABS fuses.
- Watch all four wheel speeds on the scan tool while driving slowly: a wheel that reads zero or drops out points to that sensor or its wiring.
- Inspect the sensor, wiring and tone ring at the suspect wheel.
Can you drive with the ABS light on?
Yes, carefully: the brakes work, but without anti-lock or stability control. Leave extra distance, avoid hard braking on slippery roads and repair it soon. If the red brake light is also on, or the pedal feels soft or sinks, stop driving and check the brakes; see how to bleed brakes and sticking brake caliper.
Other effects of a wheel speed fault
On some vehicles the wheel speed signal also feeds the speedometer, cruise control and transmission shift timing, so an ABS fault can come with erratic shifting or a P0500 vehicle speed code. If shifting problems continue after the sensor is fixed, see transmission control module and limp mode.
More guides: wheel bearing noise · brake pedal goes to the floor.
Trouble codes: U0121 Lost Communication With ABS · U0415 Invalid Data From ABS Module · all OBD2 codes.
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