Powertrain, shared range

P3478 Cylinder 10 Exhaust Valve Control Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Exhaust switching element at cylinder 10 stuck
Oil pressure too low for the exhaust switch
Exhaust actuator responding slowly

Symptoms

  • Check engine lamp on
  • Harsh jolt as cylinder 10 is reactivated
  • Misfire on cylinder 10 (P0310)

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

P3477P3479P3480P3474P0310

References: law.cornell.edu, patents.google.com, bentleymedia.com, media.audiusa.com.