P28DCClutch B Pressure Sensor Circuit/Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P28DC concerns the sensor that reports the hydraulic pressure acting on clutch B of a dual-clutch or hybrid transmission. The code points to a broken connection: the module receives no usable signal at all, as happens when a signal, supply or ground wire is open or the connector has come off. No manufacturer documents P28DC publicly. A Getrag patent shows why the reading matters: each clutch has its own actuator pump with a dedicated electric drive, and the measured pressure closes the loop over motor speed; an Audi patent likewise gives every clutch its own pressure sensor. CARB requires circuit checks on such inputs. Which clutch carries the letter B is up to the maker. Without the signal the module runs clutch B on a fallback or takes it out of use.
- What you may notice
- Transmission warning or check engine light on
- Gears served by clutch B blocked, transmission in emergency mode
- Jerky launch or harsh shifts
- Likely causes
- LikelyConnector at the sensor or transmission plug loose, unplugged or with a pushed-back pin
- PossibleSignal, supply or ground wire of the sensor broken
- PossiblePressure sensor internally open
- RareSensor input in the transmission control module faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €1,800
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.