Powertrain, generic (extended)

P25AC Piston Cooling Oil Control Circuit Performance/Stuck Off

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P25AC is a functional fault rather than a wiring one: the valve is told to let oil reach the piston jets, but the feedback shows no flow. GM's 18OBDG04 diesel table reads a pressure switch in the jet circuit and fails the test when that switch stays without pressure while the engine turns, main oil pressure is at least 206 kPa and the command has been held for 8 s or more; 40 of 50 samples must fail, Type B. Porsche technical information 2306 from March 2023 for the Macan four-cylinder from model year 2022 explains that P25AC00, displayed there as an implausible oil pressure switch signal, mostly stems from machining swarf jamming the control valve; a new valve, cleaning and an oil change cure it. Without cooling oil the pistons run hotter under load.

Likely causes

Valve jammed by swarf or dirt in the oil
Piston cooling pressure switch faulty or unplugged
Low oil level or weak oil pressure feeding the jet circuit
Restricted oil passage to the jets

Symptoms

  • Check engine lamp after two drives
  • Engine power reduced under high load
  • Risk of piston damage if driven hard for long periods

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

P25A9P25ADP25AE

References: gsi.ext.gm.com, static.nhtsa.gov, law.cornell.edu.