Electrical · Hackbridge, South London

ABS sensor faults proved before anything is replaced

An ABS warning light tells you a wheel speed signal has been lost. It does not tell you which part failed, and on most cars there are three candidates at each corner: the sensor, the wiring that runs to it, and the toothed or magnetic ring it reads. We work through all three at our Hackbridge workshop before we quote, because fitting a sensor to a car whose fault is a chafed harness costs you money and leaves the light on. Prices start from £89 and you get the figure in writing before we touch anything.

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From £89 · 45 minutes–2 hours
Mon–Sat 8am–8pm

Audi SQ5 in for brake and wheel-speed work at KITH Cars Garage & Bodyworks, Hackbridge

From £89Written quote before we start

45 minutes–2 hoursTypical time in the workshop

3 monthsWorkmanship warranty

17 areasCollection across South London

Tested before anything is ordered

The sensor, the circuit and the ring are each checked separately, so the part written on your quote is the part that actually failed.

You see the reading yourself

The oscilloscope trace, or a photograph of the damaged ring, is shown to you before you decide whether to go ahead.

Seized sensors freed, not snapped

A corroded sensor bonded into an aluminium hub gets heat and penetrating oil rather than brute force. Snapping one off means drilling the hub, which costs many times what the sensor does.

Wiring repaired to a standard

Where the loom is the fault we fit new cable with crimped, sealed and heat-shrunk joints, so the repair survives the salt and spray that killed the original.

In the workshop

How we handle ABS sensor replacement at Hackbridge

The car goes on the ramp and the scan comes first, but a code such as 'front left wheel speed sensor, signal implausible' names a circuit rather than a part. With an active sensor we back-probe the two wires and watch the output on an oscilloscope while the wheel is turned by hand. A healthy sensor produces a clean square wave that changes frequency smoothly with speed; a cracked encoder ring produces a trace with a gap in it at exactly the same point on every revolution. Passive sensors are checked for resistance and output amplitude instead, along with the air gap.

Then the mechanical side. The sensor comes out and we look at its tip, because a magnetic sensor collects steel swarf from a disintegrating bearing and that alone can explain a fluttering signal. With the sensor out we can see the ring through the hole, and we check the hub for play before condemning anything. On rear sensors we pay particular attention to where the harness passes into the wheel arch and along the trailing arm, flexing it while watching the live data, because a wire broken inside its insulation reads perfectly at rest and drops out over a speed bump.

You see what we saw: the trace, or a photograph taken down the sensor hole. The written quote follows that, and it names which corner, which part and how long. A few things we will not do. We will not fit a sensor on spec to find out whether it cures the light. We will not cut the plug off a universal sensor and splice it into your loom, because a soldered and taped joint in a wheel arch becomes next winter's intermittent fault. And we will not bandage a chafed harness with tape; damaged wiring gets new cable and sealed, heat-shrunk joints.

Electrical

ABS Sensor Replacement: what’s involved

Each wheel has a speed sensor that reads a toothed or magnetic ring turning with the hub or driveshaft. The ABS module constantly compares the four signals. If one wheel slows too quickly under braking, the system releases and reapplies that brake to stop it locking. The same signals feed traction control, stability control and often the speedometer, hill-hold and tyre pressure warning.

Older cars use passive sensors that generate their own signal. Most modern cars use active sensors, which are powered by the ABS module and often read a magnetic encoder built into the wheel bearing seal. Sensors sit right next to the brakes, exposed to heat, water, salt and brake dust, so corrosion, damaged wiring and failed connectors are common. When a signal drops out, the system switches ABS and stability control off and lights the warning. Your normal brakes still work.

Signs of an ABS sensor fault

ABS warning light on

A steady ABS light means the system has switched itself off. Normal braking still works, but the wheels can lock under heavy braking.

Traction and stability lights too

Because they rely on the same wheel speed signals, the traction control or ESP light usually comes on with the ABS light.

Light comes and goes

An intermittent warning, often after bumps, in wet weather or at a certain speed, usually points to damaged wiring, a loose connector or a corroded sensor.

ABS pulsing at low speed

If the pedal pulses and the ABS activates when stopping gently, a sensor may be giving a false reading from a dirty sensor or a cracked reluctor ring.

Speedometer or tyre warning faults

On cars that take road speed or tyre pressure monitoring from the wheel sensors, a faulty sensor can upset the speedometer or set a tyre warning.

Other systems disabled

Hill-hold, cruise control, stop-start and some electric parking brake functions may stop working when a wheel speed signal is missing.

When should it be done?

ABS sensors have no replacement interval. They are replaced when they fail or when their wiring is damaged. Get the car checked as soon as the ABS light comes on, because the car won't stop as well in an emergency on a wet road without ABS and stability control. An ABS warning light that stays on is also an MOT failure. Faults often show up after brake, hub or suspension work, when a sensor or its wiring may have been disturbed.

ABS, traction or stability warning light on
Intermittent warnings in wet weather or over bumps
Warning lights after brake, wheel bearing or suspension work
Before an MOT if the ABS light is showing

How we replace an ABS sensor

Check-in and symptomsWe ask when the light appears and whether any work has been done recently, as disturbed wiring after brake or suspension work is common.
Diagnostic scanWe read the ABS module fault codes to identify which wheel is affected and whether the fault is signal, circuit or plausibility related.
Live data and testingWe compare live wheel speed readings on a road test or ramp and test the sensor circuit with a multimeter or oscilloscope to separate sensor, wiring and ring faults.
Inspect the ring and bearingWe check the reluctor ring or magnetic encoder for cracks, corrosion or damage and check the wheel bearing for play, as either can cause a false signal.
Written quoteWe explain the cause and give you a written quote. If the encoder is built into the wheel bearing, we'll explain why the bearing may need replacing.
Replace the sensorWe carefully remove the old sensor, which is often seized in the hub, clean the mounting, and fit the new sensor with its wiring routed and secured correctly.
Clear codes and road testWe clear the fault codes, road test to confirm all four wheel speeds read correctly and the warning lights stay off, and run any calibration the car needs.

Parts we fit

Sensors must match the car exactly. Active and passive types are not interchangeable, and connectors and lengths vary between models and even between axles. We fit OE or OE-equivalent sensors from manufacturers such as Bosch, ATE or Continental. Where the wiring is damaged we repair it properly with sealed connectors, and where the fault is in a reluctor ring or a wheel bearing encoder, we replace that part rather than just the sensor.

OE or OE-equivalent ABS wheel speed sensors
Reluctor rings where cracked or corroded
Wheel bearings with integral magnetic encoders where required
Sensor wiring and sealed connector repairs

How long it takes

45 minutes–2 hours

A straightforward sensor swap often takes under an hour. Seized sensors, wiring repairs or a reluctor ring or wheel bearing replacement take longer. Most jobs are completed the same day.

What’s included

ABS system fault code scan
Wheel speed live data check
Sensor circuit and reluctor ring inspection
Correct replacement sensor fitted
Fault codes cleared
Road test to confirm the warning lights stay off

Worth knowing

What people get wrong about ABS sensor replacement

Replacing all four sensors

The fault codes name a corner. Changing the other three because they are the same age spends money on parts that were doing their job.

Reading the ABS light as a brake warning

The amber ABS symbol reports on the anti-lock system only. Worn pads, low fluid and the parking brake have their own separate warnings, and they mean very different things.

Jet-washing the hub to clean a sensor

A lance held close to a wheel arch drives water past connector seals and into the loom. Faults that appear a week after a thorough wash often start exactly here.

Buying a universal sensor to save money

Sensors differ in output type, resistance and cable length, and a spliced connector sits in the wettest part of the car. A pattern sensor with the correct plug costs a little more and stays fixed.

Instant quote

Price your ABS sensor replacement now

Enter your reg and we’ll look up your car, then price the job from our own labour rates and the book time for your model. Nothing is booked until you say so, and the written quote comes before any work.

Free, about 30 seconds, no sign-up
Parts, labour and VAT included
3-month workmanship warranty
Collection and delivery across South London

“It’s rare to find a garage you can truly trust. Fair price, brilliant customer service.”Thinushan K. · ★★★★★ Google

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Questions

ABS Sensor Replacement: your questions answered

What does the diagnosis cost if I decide not to go ahead?

The diagnostic time is a fixed figure, settled with you before anything is plugged in, and it sits on the written quote beside the repair. If you choose not to have the work done, you have still paid for a proper answer and the findings are yours to take wherever you like.

Will it be sorted in a single visit?

Diagnosis usually takes under an hour and many sensor replacements are finished the same morning. If the sensor is seized, the wiring needs repairing or a part has to be ordered, it is easier to leave the car with us. Local collection and delivery is there if neither suits.

Is the repair guaranteed?

Our workmanship is covered for 3 months and the sensor carries its own manufacturer's warranty. If the warning light returns and it traces back to our work or the part we supplied, bring the car in and we will put it right.

Can you fit a cheaper part if I ask?

We will always tell you what options exist for your car and what each one costs before you decide. Where there is a genuine price gap between an OE sensor and a good OE-equivalent we will show you both. What we will not do is fit a no-name part that needs its connector modifying to go in.

Is it safe to drive with the ABS light on?

The car will still brake normally, so you can usually drive it carefully to the garage. But without ABS and stability control the wheels can lock under hard braking, so leave extra distance. If the brake warning light is on as well, get advice before driving.

Will an ABS light fail the MOT?

Yes. An ABS warning light that stays on, or doesn't come on when the ignition is switched on, is an MOT failure. The same applies to the electronic stability control warning on cars that have it.

Can I just clear the code?

If the fault is still there, the ABS module will find it again, usually within a short drive. Clearing codes without finding the cause just delays the repair.

Why might I need a wheel bearing as well?

On many modern cars the magnetic ring that the sensor reads is built into the wheel bearing seal. If that encoder is damaged or the bearing has excessive play, a new sensor won't cure the fault, and the bearing has to be replaced.

Why did the light come on after my brakes were done?

ABS sensors and their wiring sit close to the brakes and hubs, so they can be knocked, stretched or left unplugged during brake or suspension work. Sometimes an old sensor that was already corroded fails when disturbed. A quick scan shows which wheel is affected.

ABS Sensor Replacement near you

We look after ABS sensor replacement for drivers right across South London. Pick your area for local prices, directions and collection:

Beddington~6 min away Carshalton~5 min away Cheam~12 min away Coulsdon~17 min away Croydon~15 min away Mitcham~8 min away Morden~12 min away Norbury~18 min away Purley~15 min away Rosehill~9 min away Streatham~20 min away Sutton~10 min away Thornton Heath~15 min away Tooting~18 min away Wallington~6 min away Wimbledon~20 min away Worcester Park~20 min away

Related work we do

Brake RepairsFrom £110 · 1–3 hoursBrake pad and disc replacement, calliper and slide pin servicing, brake fluid changes and hose and pipe repairs for all makes.Wheel Bearing ReplacementFrom £235 · 1–3 hoursDiagnosis and replacement of noisy or worn wheel bearings and hub units on all makes.Engine DiagnosticsFrom £122 · 1–2 hoursA proper diagnosis of warning lights, running faults and electrical problems, not just a code read.MOT TestingFrom £50 · 45–60 minutesClass 4 MOT testing for cars and light vans at a flat £50, under the DVSA maximum fee of £54.85, with nothing added for booking or admin.Car ServicingFrom £155 · 1–4 hoursInterim, full and major servicing for all makes, carried out to the manufacturer's schedule with the correct specification oil.Clutch ReplacementFrom £735 · 4–8 hoursComplete clutch kit replacement, including friction plate, pressure plate and release bearing or concentric slave cylinder, for manual cars and vans.