On with the red brake light, or the car feels wrong? Stop
If the traction light comes on with a red brake light, a soft or odd-feeling pedal, shaking or a big loss of power, find somewhere safe to pull over and switch off. That's no longer only a traction control problem. On a wet or gravel road with the light stuck on, slow right down, because the car may not catch a slide. If anyone is hurt or in danger, call 000.
What does traction control actually do?
It stops a wheel spinning when it loses grip. A sensor on each wheel reports how fast it's turning. If one spins faster than the others, the system brakes that wheel, cuts engine power, or both.
On most cars it's tied in with ABS and with electronic stability control (ESC, which brakes individual wheels to stop a slide). The main hardware for traction control and ABS is mostly the same, and ESC is built on top of ABS. RACV says ESC has been mandatory on new cars sold in Australia since November 2013, and on all light commercial vehicles since November 2017.
What's the light doing?
| What it means | What to do | |
|---|---|---|
| Flashing as you pull away on a wet road | The system is catching a wheel that's lost grip | Ease off the accelerator. Nothing's wrong |
| Steady, with OFF on the symbol | Traction or stability control has been switched off | Press the button. Many systems also come back on at the next start |
| Steady, no OFF, doesn't go out | A fault, or the system has shut itself down | Have the codes read soon, and drive gently |
| On with the ABS light | Often a shared part, such as a wheel speed sensor | Leave more room to stop. See ABS and brake warning lights |
| On with the engine light | An engine fault has often switched it off | Treat it as an engine problem first |
Why are the check engine light and traction control light on together?
Usually the traction light is following the engine light, not causing it. Traction control works partly by cutting engine power, through the throttle, the fuel or the spark. If the engine computer has a fault it can't rely on that, so on many cars it turns traction control off and shows both symbols.
The fault to chase is the engine one. A misfire, a sensor or a throttle fault are typical, and fixing it often clears the traction light as well. If the engine light is flashing or the car is rough, go by our engine light on page. If the car's down on power, see limp mode.
Other things that keep it on
- A wheel speed sensor, or its wiring, that's dirty, damaged or has failed.
- A steering angle sensor that needs setting again after a wheel alignment or steering work.
- Tyres that don't match, including a small spare, because the wheels then turn at different speeds.
- A low or weak battery, which can upset several of the car's computers at once.
- A fault in the ABS pump or its computer, which traction control depends on.
What will the mechanic read?
They'll connect a scan tool that reads the ABS and stability control computer as well as the engine. A basic code reader from a parts shop often sees engine codes and nothing else, so a clean result from one doesn't clear the car.
Then they test the part the code points to. With a wheel speed fault they'll often watch all four readings on a short drive to see which one drops out. Ask what the code was and what they tested. Changing a sensor on a guess can miss a broken wire.
A mechanic with a good diagnostic setup for your make suits this. For cars made from 2002, independents can buy the same service and repair information as dealers, so ask whether they have it for your car.
Worth trying yourself, and where to stop
You can
- Press the traction or stability button once, and see if an OFF symbol clears.
- Park safely, switch off and restart. A one-off glitch may clear.
- Check tyre pressures on a cold car, and that the tyres match.
- Note which other lights came on and what the road was like.
Leave to the mechanic
- Reading the ABS and stability control codes.
- Testing wheel speed sensors and their wiring.
- Setting the steering angle sensor after an alignment.
- Finding the engine fault if the engine light is on too.
Our call
Flashing on a wet roundabout: we'd ease off and think nothing of it. Stuck on, with the car feeling normal: we'd try one restart, then send the job this week and keep the trip to the mechanic short. With the engine light as well, we'd treat it as an engine job. With the red brake light or an odd pedal, we'd stop and have someone come to the car.