P25AD: Piston Cooling Oil Control Circuit Stuck On

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.

Medium severity. Can I keep driving?Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

Symptoms

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

Most likely causes

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

What to check, in order

Start with the simplest. You can tick off each step.

With the engine cold, check the coolant level; never do this when the system is hot
Use the scanner to command the movement and compare the actual position with the requested one.
Check the actual temperature in live data
Make sure the fan comes on when it should
Check the thermostat and connector
Measure the sensor and replace it if its readings do not make sense

Good to know

Repair difficulty: hard
It affects emissions.

What each character of P25AD means

P: Powertrain: engine and transmission
2: Generic code: same on every make
5: Speed and idle
AD: Specific fault in that system

Frequently asked questions

Can I keep driving with code P25AD?

Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

What causes code P25AD?

The most common causes are: valve held open by debris; broken return spring in the valve; piston cooling pressure switch stuck in the pressure position.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.