P3438Cylinder 5 Exhaust Valve Control Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P3438 describes an exhaust side of cylinder 5 that is commanded to deactivate or reactivate but does not follow, with an intact circuit. No manufacturer documents this code publicly. Two patents show why the exhaust side matters: in a GM patent application one shared valve switches the exhaust valves off, and back on, before the intake valves, so an exhaust lifter that lags breaks that order, and Ford detects an exhaust valve still opening after deactivation from exhaust pressure. If the exhaust valve keeps opening while the cylinder is off, the engine can run rough. GM's DFM engines report a cylinder whose valves stay active as P349C. The electrical codes for this channel are P3437, P3439 and P3440.
- What you may notice
- Check engine lamp on
- Roughness or noise while cylinders are switched off
- Likely causes
- PossibleExhaust lifter or rocker of cylinder 5 slow to switch
- PossibleInsufficient oil pressure for switching
- RareExhaust actuator valve sticking
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €3,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.