P3421 indicates the engine control module (PCM/ECM) has detected an open circuit in the exhaust valve control actuator (solenoid) for cylinder 3. This component is part of the variable valve timing (VVT) or cylinder deactivation system and regulates exhaust cam timing or exhaust valve operation. An open circuit means electrical current cannot flow to the actuator, so the PCM disables VVT control for that cylinder and sets the code.
The solenoid itself is the most common failure point for an open-circuit code, since internal coil windings can burn open from heat cycling and oil contamination.
Chafed, pinched, heat-damaged, or broken wires between the PCM and the solenoid are frequent causes of an open circuit, especially where harnesses contact exhaust manifolds or engine brackets.
Oil-soaked, corroded, or backed-out pins at the solenoid connector or the PCM connector interrupt the circuit and produce the same open-circuit reading as a failed solenoid.
Many VVT/exhaust control solenoids rely on clean oil at the correct viscosity; sludge or wrong oil grade can clog passages and indirectly trigger actuator circuit faults, though this more often produces performance codes than pure open-circuit codes.
A seized phaser or severe mechanical fault can stall the actuator and mimic an open circuit, but is less likely than electrical causes for this specific code.
The driver's transistor inside the PCM can fail open, but this is rare. It should only be considered after the solenoid, wiring, and connectors have all been ruled out by direct testing.
Short-term driving is usually possible, but you may notice rough running, reduced power, and worse fuel economy. Extended driving can stress the catalytic converter and cause the PCM to lock the engine into a reduced-power mode.
Almost never. P3421 is an open-circuit code, and the open circuit is located in the solenoid, its wiring, or its connector in the vast majority of cases. Replacing the PCM is costly and typically does not resolve the code. Focus diagnostic effort on the solenoid and its harness first.
No. The solenoid is the most common cause, but broken wires, corroded connector pins, or (rarely) a PCM driver fault can produce the identical code. Direct resistance and voltage testing is needed before replacing any part.
It can contribute to VVT-related drivability codes, but a pure open-circuit code like P3421 usually points to an electrical fault. Still, checking oil level and condition is a quick step that should not be skipped during diagnosis.