P3400 to P3497: cylinder deactivation system

What does P3400 mean?

Some engines shut part of their cylinders off when little power is needed, by holding those cylinders' valves closed. The valves are held by special lifters or rocker arms switched by engine oil pressure, which solenoids controlled by the engine computer send or cut. Each cylinder has codes for its intake and its exhaust valve control: a circuit that is open, low or high, or poor performance. When it finds a fault, the computer usually stops deactivating cylinders, so the engine runs on all of them and uses a little more fuel.

What causes P3400?

1. Low engine oil, or oil of the wrong grade, which the switching lifters depend on
2. A failed deactivation solenoid, or a damaged wire or connector to it
3. A collapsed or stuck switching lifter, a known wear point on some engines
4. A blocked oil screen or passage feeding the solenoids

What to check first for P3400

• Check the oil level and confirm the grade matches the owner's manual
• Note which cylinder the code names, and whether there is also a misfire code on it
• Measure the deactivation solenoid's resistance and inspect its connector
• Listen for a ticking valvetrain, a sign of a lifter that is not working properly

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