What it means
Brake Master Cylinder Piston Position Sensor B Circuit Range/Performance: the signal is implausible or outside the valid 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 implausible or outside the valid operating range, rather than simply registering as a high or low signal.
Common causes
Most likely first.
- Sensor reading drifted
- Sensor element aged beyond calibration window
- Sensor mounting loose - signal damping
Symptoms
- ABS warning light on
- ESC/stability control may be disabled
How to diagnose it
- Scan the brake module and review freeze-frame data and live sensor B readings as piston position changes to identify when the signal becomes implausible.
- Inspect sensor B's connector and wiring for corrosion, loose terminals, damaged insulation, or intermittent contact.
- Check that sensor B is mounted securely and has not shifted, which can damp or distort its reported movement.
- Compare sensor B's response with the manufacturer's expected range and procedure, checking its circuit and mounting before condemning the sensor.
- If the circuit and mounting are sound, test sensor B and the brake module input according to the manufacturer's procedure.
Common fixes
- Secure sensor B's mounting and correct its position according to the manufacturer's procedure.
- Clean and secure its connector or repair damaged wiring that makes the reading erratic.
- Replace sensor B if its reading remains outside the valid range after mounting and circuit checks.
- Repair the brake module only if its input is confirmed faulty.
Can I keep driving?
The ABS and stability systems may be disabled. Avoid high speeds and hard braking, and arrange prompt inspection because those systems may not respond as intended during a stop.
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.