P25AAPiston Cooling Oil Control Circuit Low
- 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
- P25AA flags a voltage at the piston cooling oil control valve output that sits too low for the commanded state, typically a short to ground between the module and the valve. This valve decides whether the oil jets under the pistons spray. GM's 2018 diesel engine table 18OBDG04 tests the low-side driver while it is switched off: if the output behaves like a connection of 0.5 ohm or less to ground in 40 of 50 checks taken every 100 ms, with at least 11 V from the powertrain relay, the code is stored as Type B and the lamp follows on the second trip. Deutz EMR L1 industrial engines report the same fault on their high-side switched supply valve as P25AA-11. An open circuit is P25A9, a short to power P25AB.
- What you may notice
- Check engine lamp after two drives
- Possible power limitation to protect the pistons
- Likely causes
- LikelyValve control wire chafed through and touching ground
- PossibleInternal short in the piston cooling valve
- PossibleWater or oil in the valve connector bridging the pins
- RareFaulty output stage in the engine control module
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.