Seeing the ABS and traction control lights come on together is normal — they are two functions of the same system. The traction control uses the ABS wheel speed sensors to detect a spinning wheel, so when the ABS system faults out, traction control switches off with it and both lamps light. In the vast majority of UK cars the cause is one dirty or failed wheel speed sensor, and that is a £90 to £220 repair. Your normal brakes still work; the anti-lock function and the electronic stability aids do not.
Why the two lights always appear together
ABS, traction control and electronic stability control all run off the same hardware: four wheel speed sensors, the ABS pump and modulator, and one control module. If the module loses a valid signal from any wheel, it cannot calculate slip. Rather than guess, it disables anti-lock braking and stability control and lights both warning lamps. On many cars the stability control lamp (a car with skid marks) joins them, and on some models the hill-hold, cruise control and even the electronic handbrake stop working too — all of them depend on wheel speed data. So two or three lights does not mean two or three faults. It usually means one sensor.
The causes, in the order a garage finds them
1. **Wheel speed sensor fault** — the most common by a wide margin. The sensor tip corrodes, the wiring chafes near the suspension, or the reluctor ring behind it rusts and breaks up. Codes C0035 to C0050 or manufacturer equivalents name the corner. £90 to £220 fitted. 2. **Damaged or corroded wiring** — the loom runs down the strut and flexes with every bump. Broken cores inside intact-looking insulation are common on cars over ten years old. £70 to £200. 3. **Reluctor ring** — the toothed ring the sensor reads, sometimes built into the wheel bearing. If it is part of the bearing, the whole hub is the repair: £180 to £450 per corner. 4. **Low brake fluid or a faulty brake light switch** — cheap and often overlooked; both can trigger ABS warnings on some models. 5. **ABS pump or module failure** — the expensive one. £400 to £1,200 new, though specialist repair or reconditioning of the module is often £150 to £350 and perfectly reliable. 6. **Flat or weak battery** — low voltage during cranking sets spurious ABS codes on plenty of modern cars. Charge the battery, clear the codes and see if they return before spending anything.
How it is diagnosed
A generic OBD reader often will not see these codes; ABS lives on a separate module and needs a scan tool that can access the chassis systems. Most independent garages have one. The useful test is live wheel speed data. Drive with the tool connected and watch all four wheels: the faulty corner drops out or reads erratically while the other three track together. That is a definitive result, and it takes one short road test. Expect £40 to £80 for the scan. A garage that wants to fit an ABS pump without showing you live data on all four wheels has not done the work.
Can you drive like this?
Yes — carefully, and knowing what you have lost. Your ordinary hydraulic brakes are unaffected. The car will stop. What is missing is the anti-lock function that stops the wheels locking under heavy braking, and the stability control that catches a slide. On a dry road at sensible speeds that is manageable. In heavy rain, ice, or an emergency stop, it matters a great deal, and stopping distances on a slippery surface can be significantly longer because a locked wheel steers nowhere. One firm point: an ABS warning light is an MOT failure. There is no grey area, so it has to be fixed before your next test regardless.
What it costs in the UK
| Repair | Typical fitted price | |---|---| | ABS scan and live data diagnosis | £40 – £80 | | Wheel speed sensor | £90 – £220 | | Wiring repair | £70 – £200 | | Wheel bearing with integrated reluctor | £180 – £450 | | Brake light switch | £50 – £120 | | ABS module repaired / reconditioned | £150 – £350 | | New ABS pump and module | £400 – £1,200 | The first three cover most cars that come through the door with these lights.
Before you book it in
Two things are worth checking yourself, because they cost nothing. Check the brake fluid level — a low level triggers warnings on many cars and also tells you your pads are worn or you have a leak. And check the battery, particularly if the lights appeared after a cold morning or a jump start; a voltage dip during cranking is a genuinely common cause of spurious ABS codes. If the lights came on straight after new tyres, a wheel change or suspension work, mention that immediately. A sensor knocked out of position or a cable trapped during reassembly is a five-minute fix if the garage knows to look.
Why are my ABS and traction control lights on at the same time? — Because traction control uses the ABS wheel speed sensors. When the ABS system faults, traction control is disabled with it and both lamps light. It is normally one fault, not two.
Can I drive with the ABS and traction control lights on? — Your normal brakes still work, so short journeys at sensible speeds are manageable. You have lost anti-lock braking and stability control, which matters in wet or icy conditions and in an emergency stop.
What is the most common cause? — A faulty or dirty wheel speed sensor, or its wiring. That accounts for the large majority of cases and costs £90 to £220 fitted.
Will the ABS light fail an MOT? — Yes. An illuminated ABS warning lamp is an MOT failure with no discretion, so it must be repaired before the test.
Can a flat battery cause ABS and traction control lights? — Yes — low voltage during cranking sets spurious ABS codes on many modern cars. Charge or replace the battery, clear the codes and see whether they return before replacing any parts.
How much does it cost to fix? — A sensor is £90 to £220, wiring £70 to £200, a wheel bearing with an integrated ring £180 to £450 and an ABS module repair £150 to £350. A full new pump is £400 to £1,200 but is comparatively rare.