P28EFEngine Disconnect Clutch Actuator Performance/Stuck Off
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- In a P2 hybrid a clutch placed between combustion engine and e-machine lets the car drive electrically with the engine at rest and couples the engine back in when it is needed. P28EF says the device that applies this clutch is not doing its job: it is commanded to act, but the expected pressure or clutch response stays absent, so the actuator behaves as if switched off. No manufacturer documents P28EF publicly. On Audi's A3 e-tron the clutch is applied through a pressure regulating valve in the mechatronic unit, and a mechanically faulty valve there produced the neighbouring code P2884 (clutch stuck open); a Ford patent feeds the clutch valves from hydraulic pumps. CARB counts such hybrid parts as monitored output components. The engine may then fail to join in or to start.
- What you may notice
- Engine does not start or does not engage while driving in hybrid mode
- Gearbox or hybrid system warning in the cluster
- Reduced power or electric-only limp mode
- Likely causes
- LikelyPressure regulating valve of the disconnect clutch sticking or mechanically faulty
- PossibleContaminated or low transmission fluid, so the actuator cannot build pressure
- PossibleElectric or mechanical oil pump delivers too little pressure to the clutch circuit
- RareControl software or learned clutch values out of date
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €150 – €3,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.