P25ADPiston Cooling Oil Control Circuit Stuck On
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P25AD describes the reverse mechanical failure: the piston cooling valve ought to be shut, yet oil keeps reaching the jets. GM's diesel table 18OBDG04 detects it when the pressure switch in the jet circuit reports pressure although the valve has been commanded to its off state for at least 8 s, with the engine turning and main oil pressure of at least 206 kPa; 40 bad samples out of 50 make it a Type B fault. Dirt or a broken return spring holding the valve open is the usual reason, a switch stuck closed the rarer one. The pistons are not at risk, but the jets bleed oil constantly, which can lower pressure at other consumers and lengthens warm-up after a cold start. Apart from GM, no manufacturer documents this code publicly.
- What you may notice
- Check engine lamp after two drives
- Longer warm-up in cold weather
- Slightly lower oil pressure reading at idle
- Likely causes
- LikelyValve held open by debris
- PossibleBroken return spring in the valve
- RarePiston cooling pressure switch stuck in the pressure position
- 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: €150 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.