What it means
Brake-by-wire and electronic brake systems use two redundant pedal position sensors. Their readings disagree by more than the diagnostic tolerance - one or both has drifted, or wiring picks up noise on one channel.
At a glance
- Usually lights the check-engine light
How it works
Brake pedal position sensors A and B provide redundant readings so the control module can cross-check pedal movement. This code sets when the two signals disagree beyond the permitted relationship, which can result from a drifting sensor, circuit fault, or electrical interference.
Common causes
Most likely first.
- One pedal position sensor drifting or failing
- Loose, damaged, or corroded wiring or connector
- Electrical interference affecting one sensor signal
Symptoms
- Brake or check-engine warning light may illuminate
- Brake-related assistance or stop-start functions may be limited
How to diagnose it
- Review freeze-frame data and graph sensors A and B together while slowly pressing and releasing the brake pedal.
- Check whether both readings change smoothly and maintain the expected relationship across pedal travel using the manufacturer's specifications.
- Inspect both sensor connectors and harnesses for loose or corroded terminals, damaged insulation, or wiring routed near sources of electrical interference.
- Move each harness gently while monitoring both signals to look for a dropout or sudden change that affects the correlation.
- If the circuits are sound, test each sensor separately and diagnose the channel that deviates from the manufacturer's expected relationship.
Common fixes
- Repair loose, corroded, or damaged wiring at the sensor channel causing the mismatch.
- Secure or reroute wiring that is picking up electrical interference.
- Replace the drifting or faulty pedal position sensor identified by testing.
- Repair a confirmed fault in the associated module circuit.
Can I keep driving?
The control module may limit brake assistance or stop-start when it cannot reconcile sensors A and B. If a brake warning appears or pedal feel or braking changes, stop safely and have the system checked before driving further.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.