Powertrain, shared range

P34A3 Cylinder 12 Deactivation/Intake Valve Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P34A3 closes the series at the twelfth cylinder: cylinder 12 was commanded to deactivate, but its valves did not stop. No manufacturer documents this code publicly. A dedicated check is needed because CARB's misfire definition excludes cylinders that are deliberately shut off, so the misfire monitor will not flag a skipped cylinder that still pumps air without fuel. Delphi's patent US7314034B1 confirms the state of each cylinder from the pattern of intake or exhaust pressure pulses, close to the principle GM applies to cylinders 1 to 8. On V12s that switch bank by bank, a defect would first show as rough running and a warning lamp. P3490 handles the control side of cylinder 12.

Likely causes

Lifter or rocker switching element of cylinder 12 stuck
Oil control valve of the deactivation sticking
Low or aged oil

Symptoms

  • Check engine lamp on
  • Rough running at light load
  • Higher fuel use

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€150–6,000
Time1–16 h

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

Parts involved

liftervalve traincylinder deactivation solenoidengine oil

Related codes

P3490P3489P34A2P34A0P0312

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