Powertrain, generic (extended)

P25AD Piston Cooling Oil Control Circuit Stuck On

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Valve held open by debris
Broken return spring in the valve
Piston cooling pressure switch stuck in the pressure position

Symptoms

  • Check engine lamp after two drives
  • Longer warm-up in cold weather
  • Slightly lower oil pressure reading at idle

Repair estimate

DifficultyHardWorkshop job
Parts and labour€150–900
Time1–4 h

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

Parts involved

piston cooling solenoid

Related codes

P25A9P25ACP25AA

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