P3478Cylinder 10 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
- P3478 describes a cylinder 10 exhaust valve that does not switch as commanded although its actuator circuit is fine. No manufacturer documents this code publicly; J2012 reserves the codes for cylinders 9 to 12 for engines with more than eight cylinders. When an exhaust valve keeps working after shut-off, the trapped gas is pumped out and the cylinder cools, which a Ford patent proposes to catch through exhaust pressure. Cooling is also why Bentley alternates the idle bank of its W12 to protect cylinders and converter; Bentley, like Audi on the R8 V10, shuts down banks rather than individual valves. The code therefore only applies to engines with switchable exhaust valves, which none of the known V10 or V12 systems publicly use. P3477, P3479 and P3480 are the electrical faults.
- What you may notice
- Check engine lamp on
- Harsh jolt as cylinder 10 is reactivated
- Misfire on cylinder 10 (P0310)
- Likely causes
- PossibleExhaust switching element at cylinder 10 stuck
- PossibleOil pressure too low for the exhaust switch
- RareExhaust actuator responding slowly
- 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.