Generic fault code

C0634 — Brake pressure sensor A/B: correlation fault

Q: What usually causes code C0634?

Faulty, aged or drifting sensor. The most likely causes come first. Only a check on the car confirms which one is yours.

Q: What are the symptoms of code C0634?

ABS, ESP or brake warning lights on. ABS and stability control switched off; normal braking usually still works. On some cars, the speedometer or driver aids failing. These are the usual symptoms of this kind of fault: not all of them always appear, and sometimes you notice nothing.

The control unit stores code C0634 when it detects this fault: “Brake pressure sensor A/B: correlation fault”.

Indicative severity: HighBrakes and stability

Updated on October 13, 2026

Reviewed by Daniel Morales, founder of Reprorace SL, on October 13, 2026

What does code C0634 mean?

ABS, stability control and their sensors (wheel speed, brake pedal, pressure). With a fault here, ABS or stability control may be switched off.

System: C · Chassis
Area: Brakes and stability · Car system: Brakes, ABS and ESC
Type: Generic (SAE J2012 / ISO 15031-6): the same meaning on every make
Indicative severity: High. Diagnose as soon as possible: it may affect safety or cause damage (engine, catalyst, brakes).

What usually causes code C0634?

Faulty, aged or drifting sensor

The most likely causes come first. Only a check on the car confirms which one is yours.

What are the symptoms of code C0634?

ABS, ESP or brake warning lights on
ABS and stability control switched off; normal braking usually still works
On some cars, the speedometer or driver aids failing

These are the usual symptoms of this kind of fault: not all of them always appear, and sometimes you notice nothing.

Can I keep driving with code C0634?

Better not, except when you really have to. This fault may affect safety or damage the engine, the catalytic converter or the brakes. See a workshop as soon as possible; if you must move the car, drive gently and only short distances. If the light flashes, the car loses power, makes unusual noises or the brakes or steering feel different, stop somewhere safe and call for assistance.

This is guidance only: only someone who checks the car can say whether it is safe to drive.

An indicative description of the code's generic meaning. Each manufacturer may give it a different meaning, conditions or tests: always follow its service information and your workshop's advice.

What you can do yourself

For this kind of fault

Keep a longer distance and avoid hard braking: without ABS the wheels can lock. If the red brake light comes on or the pedal feels different, stop and call for assistance.

Read the code and keep the report: with an ECO-LITE in the OBD socket you see it on your phone or computer, with the data captured when the fault happened.
Look for anything obvious: a loose connector, a disconnected hose, a fuel cap not closed properly or a low fluid level. Do not take apart anything you do not know.
Clear the code only after writing it down or after the repair. Clearing turns the light off, but it also deletes the freeze-frame data and the readiness monitors used at the inspection.
Drive normally for a few days and read the codes again. If the code comes back, the fault is still there: book the workshop and bring the report.

Read your car's fault codes on your phone

With an ECO-LITE in the OBD socket you see the codes in your account, with the data captured when the fault happened, and your workshop can check them remotely, always with your permission.

See the ECO-LITE Reserve (presale)

Related codes

C062CBrake booster motor B: performance
C062DABS valves: range/performance
C0649Brake pressure sensor M, circuit open
C064ABrake pressure sensor M, circuit: signal high
C064BBrake pressure sensor M, circuit: signal low
C064CBrake pressure sensor M: range/performance

C06xx codes: steering, brakes and wheel speed sensors

All fault codes