P3400: Cylinder Deactivation System — what it means, the affected system and what to check before replacing parts.
Meaning, symptoms, causes and checks
The cylinder deactivation system has reported a fault. This is not the same as an individual-cylinder misfire and does not specify which valve actuator or control path is responsible. The supported cylinder-deactivation arrangement depends on the engine.
Affected system: Cylinder deactivation control
Symptoms
- An engine warning may appear together with rough running or reduced power.
- Fuel use may rise when cylinder deactivation does not operate as intended; some drivers may feel no other change.
Possible causes
- Low oil level, unsuitable oil or inadequate oil pressure may interfere with oil-operated cylinder-deactivation mechanisms.
- Faulty deactivation-control solenoids, damaged wiring or an actuator-control fault may prevent the expected state change.
What to check
- Confirm P3400 and related engine codes and identify the cylinder-deactivation system used by this engine.
- Check the engine-oil level and condition and inspect relevant actuator-control connectors.
- Compare cylinder-deactivation commands and available feedback with the manufacturer's service data before testing solenoids or internal mechanical parts.
Also written as: P3400-00, P340000 (some scan tools add the fault-type byte, e.g. -00).