Cylinder 3 Deactivation/Intake Valve Control Circuit High
Diagnostic trouble code P3420 indicates that the powertrain control module (PCM) has detected an unexpectedly high electrical voltage in the control circuit for the cylinder 3 deactivation or intake valve solenoid. This typically means the circuit is shorted to power or has high resistance, preventing the system from properly deactivating cylinder 3 for fuel economy.
While not immediately dangerous, this issue can cause poor engine performance, reduced fuel economy, and potential long-term wear if the cylinder deactivation system malfunctions. It should be diagnosed and repaired soon to restore proper engine operation.
Common symptoms
- Illuminated Check Engine Light
- Noticeable decrease in fuel economy
- Engine running rough or vibrating, especially at cruising speeds
- Lack of engine power or hesitation during acceleration
- Abnormal or harsh transitions between cylinder deactivation modes
Likely causes
- Low engine oil level or dirty engine oil
- Faulty cylinder 3 deactivation/intake valve control solenoid
- Damaged, corroded, or loose wiring and connectors in the solenoid circuit
- Short to voltage in the control circuit wiring
- Restricted oil passages leading to the deactivation solenoid
- Faulty Powertrain Control Module (PCM)
What to check before replacing parts
Check the engine oil level and condition.
Look for: Ensure the oil is at the correct level and not excessively dirty or sludged, as cylinder deactivation systems rely heavily on proper oil pressure and clean oil to function.
Visually inspect the wiring harness and connectors for the cylinder 3 deactivation solenoid.
Look for: Look for frayed wires, melted insulation, corrosion, or loose connections that could cause a short to voltage or high resistance.
Test the cylinder 3 deactivation solenoid resistance using a multimeter.
Look for: Compare the measured resistance to the manufacturer's specifications; an out-of-limits reading indicates an internally failed solenoid.
Check the control circuit for a short to voltage.
Look for: With the solenoid disconnected and the key on, check for unexpected battery voltage on the control wire, which would confirm a short to power in the harness.
Perform an engine oil pressure test.
Look for: Verify that the engine is producing sufficient oil pressure according to factory specifications, as low pressure can prevent the deactivation lifters/solenoids from operating correctly.
This page explains the generic P3420 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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