What it means
Brake master cylinder piston position sensor B signal voltage above expected range.
At a glance
- Usually lights the ABS or stability-control warning light
- The engine or gearbox may go into limp mode
How it works
Brake master cylinder piston position sensor B reports piston movement to the brake control module. This code sets when sensor B's signal is higher than the expected range, indicating a high signal on sensor B's circuit.
Common causes
Most likely first.
- Signal wire shorted to voltage
- Sensor B internally faulty
- Connector corrosion or damage causing a high signal
- Control module fault
Symptoms
- ABS warning light on
- ESC/stability control may be disabled
How to diagnose it
- Scan the brake module for related codes and review freeze-frame data and live sensor B readings to confirm whether the high signal is steady or intermittent.
- Inspect sensor B's connector for corrosion, moisture, damaged terminals, or a loose fit.
- Trace sensor B's harness for damaged insulation or contact with a powered wire, then gently move it while watching the live reading.
- Use vehicle wiring information to test sensor B's signal circuit for a short to voltage and check its supply and ground against the manufacturer's specification.
- If the wiring checks pass, test sensor B and the brake module input according to the manufacturer's procedure.
Common fixes
- Clean and secure sensor B's connector and repair damaged terminals.
- Repair chafed wiring or a sensor B signal wire shorted to voltage.
- Replace sensor B if it fails the manufacturer's test.
- Repair or replace the brake module only if its input is confirmed faulty.
Can I keep driving?
ABS and stability control may be disabled, and brake assist may be reduced. Avoid high speeds and hard braking; stop and arrange prompt inspection if braking feel or performance changes.
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.