P28DBClutch B Motor Position Sensor Circuit Range/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- P28DB flags a rotor position signal for the clutch B motor that is electrically present but fails the plausibility tests: angle steps arrive in a wrong order, a transition is skipped, or the derived speed disagrees with the phase currents and the measured clutch pressure. CARB 13 CCR 1968.2 calls for such rationality monitoring of input signals where it is technically feasible, beyond pure circuit checks. Interference through a damaged screen, a wire strand partly broken, a sensor or target magnet that has shifted, or metallic debris on the target are typical findings. Because commutation then goes wrong, the motor may judder or stall and P28D8 or P28D9 can follow. P28DA is the hard circuit fault, P28CC the clutch A twin. No carmaker documents P28DB.
- What you may notice
- Clutch B engages roughly or drops out intermittently
- Transmission warning, sometimes only after several trips
- Motor speed codes for clutch B stored alongside
- Likely causes
- LikelyElectrical interference through a damaged screen on the sensor lead
- PossiblePartly broken strand in the clutch B position sensor wiring
- PossibleSensor or target magnet shifted, or metallic debris on the target
- 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: €80 – €1,300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.