C0644 code meaning
Brake Pressure Sensor K Range/Performance
What C0644 means
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.
C0644 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 4 hours
- Clears after repairAfter a drive cycle
Symptoms of C0644
- ABS and ESC lamps on until a later successful check
- Stability control reduced, pedal may feel different in fallback mode
Common causes of C0644
- Most 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
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Brake pressure sensor k
What each part of C0644 means
| C | Chassis system: brakes, ABS, steering and suspension. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 44 | The exact fault in that area. |
What to do next
- Note C0644 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about C0644
What does C0644 mean?
C0644 means "Brake Pressure Sensor K Range/Performance". The voltage from sensor K is in range, yet the pressure is not believable. It is a generic code, so it means the same on every make.
Is it safe to drive with C0644?
Drive gently and only to a workshop. With C0644 the car can go into limp mode (reduced power) to protect itself.
Will C0644 fail an emissions test?
C0644 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is C0644 to fix?
Difficulty: hard. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will C0644 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.