Powertrain, shared range

P3494 Cylinder 12 Exhaust Valve Control Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P3494 is set when the exhaust valve of cylinder 12 does not follow its command although the actuator circuit is electrically intact. No manufacturer documents this code publicly; J2012 reserves the codes for cylinders 9 to 12 for engines with more than eight cylinders. Valve-based shut-off traps a charge in the cylinder; if the exhaust valve keeps opening, that cushion leaks away, which a Ford patent proposes to detect through exhaust pressure, and if it sticks shut on reactivation, compressed gas loads the valve train. The Aventador V12 and Bentley W12 sidestep this by bank shut-off without published valve switching, and for the Mercedes M137 with its hydraulic solenoid pack no public code assignment is known. Electrical faults of this actuator: P3493, P3495, P3496; intake function: P3490.

Likely causes

Exhaust switching element at cylinder 12 sticking
Oil pressure or quality insufficient for the exhaust switch
Exhaust actuator sluggish

Symptoms

  • Check engine lamp on
  • Jolt or knock on reactivation of cylinder 12
  • Misfire on cylinder 12 (P0312)

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

P3493P3495P3496P3490P0312

References: law.cornell.edu, patents.google.com, en.wikipedia.org, newatlas.com.