ABS — anti-lock braking system fault
The red ABS icon signals that the anti-lock braking system has been deactivated. Standard braking still works, but under emergency braking wheels can lock — vehicle controllability during a hard stop will be limited.
What this indicator means
The ABS system uses a wheel-speed sensor on each wheel and a hydraulic modulator to prevent lock-up. The indicator turns on when the ABS ECU loses a sensor signal, detects a modulator fault or an electronic failure. Faults are read as U-codes (U0121) or C-codes (C0035–C0050).
Common causes
- Damaged or contaminated wheel-speed sensor
- Broken wire between the sensor and the ABS module
- Discharged battery or low system voltage
- ABS hydraulic modulator failure
- CAN-bus problems (U0121 — communication loss)
- Pad replacement without ABS adaptation reset
What to do as a driver
Read C-codes and U-codes via an OBD-II adapter — they precisely identify the source. Most cases trace to a single-wheel sensor. Check the battery: below 11.5 V the ABS module often throws false faults.
Safety
You can continue driving, but avoid hard braking and icy roads. Repair within a few days.