Why is a rear wheel speed sensor fault more expensive than a front one?

Because of how the rear corner is usually built. At the front, the sensor reads a separate toothed ring pressed onto the driveshaft or hub, and the sensor is a small part that unbolts. At the rear, many manufacturers magnetise the wheel bearing's own rubber seal into alternating poles and let the sensor read that. The encoder is therefore part of the bearing, is not sold separately, and cannot be repaired, so a failed rear encoder means a complete hub or bearing assembly. Establish which type your car uses before accepting a quote.

Can a worn wheel bearing cause an ABS light?

Yes, in two separate ways, and rear bearings are the usual offenders. A worn bearing lets the hub move relative to the sensor, so the air gap opens and closes as the wheel turns and the signal becomes unreliable. On bearings with an integrated magnetic encoder, the wear and contamination that destroy the bearing also destroy the encoder. This is worth knowing at MOT time, because excessive play in a wheel bearing is a defect the tester checks for directly, quite apart from the ABS lamp.

Will a rear ABS sensor fault fail an MOT?

Yes. A brake system warning device indicating a malfunction is a major defect with 85,196 recorded failures in the DVSA data behind this site, and it applies regardless of which corner is at fault. There is a good chance of a second defect on the same visit, because the tester checks each wheel for bearing play by hand and a worn rear bearing is one of the commonest causes of this code.

Why won't my electronic parking brake release with C0045?

Because on many cars the parking brake and hill-hold logic depend on knowing whether the rear wheels are turning. Without a trustworthy rear wheel speed signal, the module cannot confirm the car is stationary or moving as expected, so it disables the automatic release and sometimes the automatic application too. It is a consequence of the sensor fault rather than a separate problem with the parking brake, and it normally resolves once the wheel speed signal is restored.

Chassis code · standard

C0045Rear left wheel speed sensor not reading

Standard definition: Left Rear Wheel Speed Sensor Circuit Malfunction

Last updated 27 July 2026

Quick answer

The ABS module cannot read the wheel speed sensor at the rear left. The detection is the same as at the front, but the repair often is not: on a great many modern cars the rear sensor is built into the wheel bearing, so the fix is a hub assembly rather than a sensor.

How the car works this out

As at the front, the ABS module checks the circuit electrically and cross-checks the corner's speed against the other three. What differs at the rear is the hardware being checked. Many manufacturers do away with a separate toothed ring and instead magnetise the rubber seal of the wheel bearing itself into alternating poles, which the sensor reads. That encoder is part of the bearing and cannot be replaced separately, so a rear wheel speed fault has a different set of likely answers even though the code looks identical to its front-axle counterpart.

What you might notice

ABS and stability control lamps on
Electronic parking brake refusing to release automatically, or hill-hold not working
Traction control cutting in oddly, or not at all
Speedometer unaffected on many cars, because road speed is often taken from the front axle
A rumble or drone from the rear that changes with cornering, if the bearing is the cause

What causes it

Most likely first. A code names the check that failed, not the part that failed it, so more than one of these can produce the same number.

1A failed magnetic encoder in the wheel bearing seal, which is not sold separately from the bearingCommon
How to check: Ask the garage to check the encoder with a magnetic viewing card, which shows the alternating poles as stripes. A blank or patchy pattern means the encoder is dead and the hub needs replacing.
2A worn rear wheel bearing, which both damages the encoder and creates play that varies the air gapCommon
How to check: Rock the wheel and listen for a rumble on a road test. Bearing play is a separate MOT defect, so this finding matters twice.
3Damaged wiring along the trailing arm or axle beam, where the loom is exposed to road spray, salt and stone chipsCommon
How to check: Follow the cable from the hub to the body. Rear runs are longer and more exposed than front ones, and the section that flexes with suspension travel is where breaks occur.
4A corroded connector, often in the rear wheel arch or above the fuel tank areaPossible
5An encoder demagnetised by a bearing being pressed in with a magnet-based tool, or by a bearing fitted the wrong way round at a previous repairPossible
How to check: Ask when the bearing was last replaced. An encoder ring fitted facing outwards instead of towards the sensor is a classic and frustrating repeat fault.
6A failed sensorPossible

What to do about it

1Establish whether your car uses a separate sensor and tone ring or a bearing-integrated encoder before agreeing to any work. It is the difference between a modest job and a hub assembly.
2Have the encoder checked with a magnetic viewing card if the bearing type is used. It is a quick test that tells you immediately whether the bearing is the problem.
3Inspect the loom along the trailing arm. Rear cable runs take more punishment from road spray and salt than front ones and are a common cause on older cars.
4Check the bearing for play and noise at the same time. A worn rear bearing is both the likely cause and a separate MOT defect, and finding it now avoids paying twice for the same wheel to come off.
5Ask about the electronic parking brake before booking. On some cars the rear hub cannot be worked on without the parking brake motors being wound back with a diagnostic tool, which affects who can do the job.

Can you keep driving?

Briefly, gently

Normal braking is unaffected, as at the front, but there is an extra consideration at the rear. If the cause is a worn wheel bearing rather than a sensor or a wire, then a mechanical part is failing, and a badly worn rear bearing can seize or allow enough movement to affect how the car handles. Listen for a rumble that changes as you sweep left and right on a quiet road, and if you can hear one, treat the repair as urgent.

Will it fail an MOT?

The lamp is the same major defect as at the front axle: a brake system warning device indicating a malfunction, 85,196 recorded failures, with DVSA using identical wording for the anti-lock and electronic braking systems so the certificate may not specify which. What makes a rear corner different is the second defect that so often comes with it. Excessive play in a wheel bearing is a defect the tester checks by hand on every wheel, and because rear wheel speed faults are so frequently caused by the bearing, a car presented with this code stands a real chance of collecting both.

The light this turns on

ABS warning lightThe anti-lock braking system has found a fault and switched itself off. Your brakes still work exactly as they always did in normal driving — what you have lost is the system that stops the wheels locking and the steering going light under a hard, emergency stop.

Common questions

Why is a rear wheel speed sensor fault more expensive than a front one?: Because of how the rear corner is usually built. At the front, the sensor reads a separate toothed ring pressed onto the driveshaft or hub, and the sensor is a small part that unbolts. At the rear, many manufacturers magnetise the wheel bearing's own rubber seal into alternating poles and let the sensor read that. The encoder is therefore part of the bearing, is not sold separately, and cannot be repaired, so a failed rear encoder means a complete hub or bearing assembly. Establish which type your car uses before accepting a quote.
Can a worn wheel bearing cause an ABS light?: Yes, in two separate ways, and rear bearings are the usual offenders. A worn bearing lets the hub move relative to the sensor, so the air gap opens and closes as the wheel turns and the signal becomes unreliable. On bearings with an integrated magnetic encoder, the wear and contamination that destroy the bearing also destroy the encoder. This is worth knowing at MOT time, because excessive play in a wheel bearing is a defect the tester checks for directly, quite apart from the ABS lamp.
Will a rear ABS sensor fault fail an MOT?: Yes. A brake system warning device indicating a malfunction is a major defect with 85,196 recorded failures in the DVSA data behind this site, and it applies regardless of which corner is at fault. There is a good chance of a second defect on the same visit, because the tester checks each wheel for bearing play by hand and a worn rear bearing is one of the commonest causes of this code.
Why won't my electronic parking brake release with C0045?: Because on many cars the parking brake and hill-hold logic depend on knowing whether the rear wheels are turning. Without a trustworthy rear wheel speed signal, the module cannot confirm the car is stationary or moving as expected, so it disables the automatic release and sometimes the automatic application too. It is a consequence of the sensor fault rather than a separate problem with the parking brake, and it normally resolves once the wheel speed signal is restored.

Check any vehicle's MOT history

Free, instant, and straight from DVSA records. No sign-up.