Failed or sticking exhaust valve control solenoid, which regulates oil flow to the valve actuator; Clogged or restricted oil passage or screen feeding the valve control system; Worn or damaged exhaust valve rocker arm or actuator mechanism; Electrical fault in the valve control solenoid circuit, such as an open or shorted wire; Contaminated engine oil or sludge buildup causing solenoid malfunction; Mechanical wear in the variable valve timing phaser or associated components; Faulty powertrain control module, though this is rare and should be considered last

DTC codes / P34xx · Auxiliary emission controls / P3478

P3478Cylinder 10 Exhaust Valve Control Performance

Q: What does code P3478 mean?

Cylinder 10 Exhaust Valve Control Performance. P3478 indicates that the powertrain control module has detected a performance fault in the exhaust valve control system for cylinder 10, typically on engines with variable valve timing or cylinder deactivation. The computer monitors the valve's response to commanded changes and sets this code when the actual position or timing deviates from the expected value beyond a calibrated threshold.

P3478 indicates that the powertrain control module has detected a performance fault in the exhaust valve control system for cylinder 10, typically on engines with variable valve timing or cylinder deactivation. The computer monitors the valve's response to commanded changes and sets this code when the actual position or timing deviates from the expected value beyond a calibrated threshold.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaAuxiliary emission controls

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Rough idle or misfire sensation, especially when the engine is cold or under light load
Reduced engine power or sluggish acceleration due to improper exhaust valve timing
Increased fuel consumption as the engine compensates for poor breathing
Audible ticking or tapping from the valve cover area if a mechanical fault is present
Intermittent stalling or hesitation during deceleration

Common causes, most likely first

Failed or sticking exhaust valve control solenoid, which regulates oil flow to the valve actuator
Clogged or restricted oil passage or screen feeding the valve control system
Worn or damaged exhaust valve rocker arm or actuator mechanism
Electrical fault in the valve control solenoid circuit, such as an open or shorted wire
Contaminated engine oil or sludge buildup causing solenoid malfunction
Mechanical wear in the variable valve timing phaser or associated components
Faulty powertrain control module, though this is rare and should be considered last

How to diagnose and fix it

Verify the code with a scan tool and check for any related codes in the valve control or camshaft position systems
Inspect the engine oil level and condition; change oil and filter if sludge or contamination is evident
Test the exhaust valve control solenoid for resistance and function according to the manufacturer's specifications
Check the wiring and connectors at the solenoid for corrosion, loose pins, or damage
Remove and clean the solenoid and its oil screen to remove debris, then retest operation
Perform a mechanical inspection of the rocker arm and valve actuator for wear or binding
If all else fails, consult a factory service manual for specific diagnostic procedures and component replacement

Oil quality and solenoid screens matter

A clogged oil screen in the solenoid is a frequent cause that many technicians overlook when replacing the solenoid itself.
The code can be set by a momentary electrical glitch that does not affect drivability, so always check for pending codes and freeze-frame data before condemning parts.
On engines with cylinder deactivation, a faulty lifter or collapsed valve can mimic a solenoid failure, leading to unnecessary solenoid replacement.
Low oil pressure or a failing oil pump can starve the valve control system and set this code without any electrical fault.
After repairs, the code may require a specific drive cycle or relearn procedure to clear and verify the fix.

Can I keep driving with P3478?

You can generally continue driving with this code, but avoid heavy acceleration or towing until it is repaired, as prolonged operation with faulty exhaust valve control may lead to catalytic converter damage or engine misfire.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.