P34A3Cylinder 12 Deactivation/Intake Valve 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
- 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.
- What you may notice
- Check engine lamp on
- Rough running at light load
- Higher fuel use
- Likely causes
- LikelyLifter or rocker switching element of cylinder 12 stuck
- PossibleOil control valve of the deactivation sticking
- PossibleLow or aged oil
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €150 – €6,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.