C0644Brake Pressure Sensor K Range/Performance
- Generic OBD-II code · Chassis
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- The voltage from sensor K is in range, yet the pressure is not believable. Bendix's EC-80 stores a plausibility error when the primary and secondary brake demand sensors disagree and asks for a static calibration after an ECU swap. Mercedes' SBC repeats self-tests about every 16 brake applications, pressurising the calipers to check sensors, valves and leaks; if the system fails, two valves stay open so pedal force acts on the brakes directly. A Bosch patent keeps an offset fault stored, with ABS and ESC lamps lit, until a later good check on a roughly straight drive passes. No manufacturer documents C0644 or says which sensor K is. Look for drift, air, a leak or a valve that does not close.
- What you may notice
- ABS and ESC lamps on until a later successful check
- Stability control reduced, pedal may feel different in fallback mode
- Likely causes
- LikelySensor K offset or gain drifted
- PossibleSensor values not re-learned after module replacement
- PossibleLeak, air or a valve that does not seal distorting the pressure
- Repair
- Hard · Usually a job for a workshop.Typical cost: €80 – €2,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.