A fault code doesn’t yet mean the unit or sensor itself is faulty: often it’s the plug and connector leading to it.
Possible causes
- The sensor was replaced or removed and its home position wasn’t learned
- The brake pedal position sensor or its connector by the pedal
- ECU (rarely)
What you can do yourself
- Cruise control, ESP and traction control may not work. The brakes work as usual.
- The suffix 4B (C0277 4B) means the sensor’s home position hasn’t been learned: it is learned with a scanner.
- If the brake pedal sensor was replaced or removed, or the body or engine unit replaced or reprogrammed, the sensor’s home position must be learned with a scanner (on GM — in both units).
- Check that the brake lights come on when you press the pedal: if not, check the brake light fuse and the sensor connector by the pedal.
Stop and don’t drive on if:
- The red brake light is on, or the brake pedal feels soft or sinks
- The steering became very heavy, or the car pulls to one side when braking
OOleg’s tip: check the connector
Often the cause is simple — there is no contact in the connector (plug). Look at the connector from the back: remove the rubber seal and you will see whether a wire is corroded or has come off completely. Corrosion shows up as green deposits. Ideally, gently pull each wire towards you one at a time: a sound wire stays in place, while a corroded one simply comes off — it needs to be repaired.
Unplug and inspect connectors with the ignition off.
This is the GM meaning (Chevrolet, Cadillac, GMC). On other makes this number means something else: if your car isn’t made by GM, change the make at the top.
Source: GM PIT5122D (static.nhtsa.gov)
The explanation comes from the error code reference in the AvtoElektrik PRO app.