Powertrain, shared range

P3438 Cylinder 5 Exhaust Valve Control Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Exhaust lifter or rocker of cylinder 5 slow to switch
Insufficient oil pressure for switching
Exhaust actuator valve sticking

Symptoms

  • Check engine lamp on
  • Roughness or noise while cylinders are switched off

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–3,500
Time0–12 h

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

Parts involved

cylinder deactivation solenoidlifterengine oil

Related codes

P3437P3439P3440P3434P349C

References: law.cornell.edu, patents.google.com, patents.google.com.