Warning lights
ABS or ESP warning light on: what it means and what to do
With the ABS or ESP light on, the car brakes normally, but without the help that stops the wheels from locking or the car from skidding. In the wet, on ice or in an emergency stop the difference is large.
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Reviewed by Daniel Morales, founder of Reprorace SL, on
Is it serious? Can I keep driving?
Carefully, and only as far as the garage. Drive slower and leave more distance, especially in the rain, and get to a garage soon. If the red brake warning light comes on at the same time, brake force distribution may fail too: stop as soon as it is safe.
A careful, general answer: only someone who inspects the car can say whether it is safe to drive. When in doubt, stop somewhere safe and call for assistance.
Most likely causes
- Wheel speed sensor: the most common cause: a dirty or faulty sensor, or a damaged cable near the wheel.
- Reluctor ring or wheel bearing: a cracked ring or a bearing with play gives an irregular signal.
- Brake pedal switch or steering angle sensor: ESP needs both signals; the steering sensor sometimes needs calibrating after a wheel alignment.
- Low voltage: a weak battery can light ABS and ESP together.
- Hydraulic unit or its control unit: less common, and more expensive to repair.
Listed from more to less common in general; on your car they may be different. A fault-code reading and a check at the garage confirm which one it is.
To understand it better: What do U codes and lost communication (U0100) mean? What does a pending, stored or permanent code mean?
Car system: Brakes, ABS and ESC
What you can check yourself
Make sure you have not switched ESP off with its button: many cars show the same symbol.
Stop, switch the car off for a minute and restart: if the light comes back, the fault is still present.
Check that all four tires have the right pressure and the same size.
With the car parked, look for a loose or broken cable near any of the wheels.
Safe checks only: with the engine off and cold whenever you look under the hood, without taking anything apart and without touching hot or moving parts.
Related fault codes
- C0035Right front wheel speed sensor supply: malfunction
- C0040Brake pedal switch A: malfunction
- C0045Brake pressure sensor B: malfunction
- U0121Lost communication with anti-lock brake system (ABS) control module A
- U0126Lost communication with steering angle sensor module
Generic codes that often come with this symptom. Seeing one does not confirm the cause: it is where the diagnosis starts.
How the ECO-LITE helps diagnose it
Plugged into the OBD socket, the ECO-LITE reads the fault codes of the control units that answer, with the freeze-frame data captured when the fault happened, and shows live data on your phone or computer. With your permission, your garage can see them remotely before you bring the car in.
What to look at here: the speed of each wheel and of the vehicle (if the ABS unit reports it), C and U codes from the brake control unit and system voltage.
Frequently asked questions
Does the car still brake with the ABS light on?
Yes, the brakes work, but the wheels can lock under hard braking. Leave more distance and avoid sudden stops.
Why do ABS and ESP come on together?
Because ESP uses the ABS wheel sensors: if ABS fails, ESP is switched off too.
Can it be the sensor of a single wheel?
Yes, and that is the most common case. The fault code usually says which wheel, for example C0035 for the front right.
Keep reading
- Brakes, ABS and ESC: how they work and what fails
- Red brake warning light on: what it means and what to do
- Heavy steering or steering warning light on: what to do
- Tire pressure warning light on: what to do
- Car symptoms: what they mean and what to do
- Check engine light on: what to do
- How to read and clear your car's fault codes
- OBD fault codes: what each one means