Powertrain, generic (extended)

P25AA Piston Cooling Oil Control Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

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.

Likely causes

Valve control wire chafed through and touching ground
Internal short in the piston cooling valve
Water or oil in the valve connector bridging the pins
Faulty output stage in the engine control module

Symptoms

  • Check engine lamp after two drives
  • Possible power limitation to protect the pistons

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–600
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

piston cooling solenoidwiring harness

Related codes

P25A9P25ABP25ACP25AD

References: gsi.ext.gm.com, serdia.deutz.com, law.cornell.edu.