Cylinder 3 Exhaust Valve Control Circuit/Open
Diagnostic trouble code P3421 indicates that the powertrain control module (PCM) has detected an open circuit or malfunction in the exhaust valve control circuit for cylinder 3. This code is typically associated with cylinder deactivation systems, where the PCM commands the exhaust valve to remain closed to improve fuel economy, but the circuit is not responding as expected.
While the vehicle can usually still be driven, the cylinder deactivation system will be disabled, leading to reduced fuel economy. It should be diagnosed and repaired soon to prevent potential engine performance issues or secondary damage.
Common symptoms
- Illuminated Check Engine Light
- Decreased fuel economy
- Engine misfires or runs rough
- Lack of engine power
- Cylinder deactivation system disabled
Likely causes
- Faulty cylinder 3 exhaust valve control solenoid
- Wiring harness damage (open or short) in the exhaust valve control circuit
- Poor electrical connection at the valve control solenoid connector
- Low engine oil level or low oil pressure
- Restricted oil passages affecting the cylinder deactivation system
- Faulty Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Check the engine oil level and condition.
Look for: Ensure the oil is at the correct level and is clean. Low or dirty oil can prevent the hydraulic cylinder deactivation lifters/solenoids from operating correctly.
Visually inspect the wiring and connector for the cylinder 3 exhaust valve control solenoid.
Look for: Look for frayed wires, melted insulation, corrosion, or loose pins in the connector that could cause an open circuit.
Test the resistance of the cylinder 3 exhaust valve control solenoid using a multimeter.
Look for: Compare the measured resistance to the manufacturer's specifications. An infinite reading (OL) indicates an internal open circuit in the solenoid.
Check for voltage and ground at the solenoid connector with the ignition on.
Look for: Verify that the circuit is receiving the proper reference voltage and has a good ground. Lack of voltage indicates a wiring issue back to the PCM or relay.
Perform an oil pressure test.
Look for: Verify that the engine is producing sufficient oil pressure according to factory specifications, as the deactivation system relies on adequate oil pressure to function.
This page explains the generic P3421 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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