Failed cylinder 3 deactivation solenoid or intake valve control solenoid (open internal coil); Open circuit in the control wire between the PCM and the solenoid, such as a broken wire or corroded connector; Short to voltage on the control circuit, often from chafed wiring near hot or moving components; Poor electrical connection at the solenoid or PCM connector, including loose pins or water intrusion; PCM driver circuit failure, though this is less common than wiring or solenoid faults; Aftermarket electrical accessories improperly tapped into the circuit causing voltage spikes

DTC codes / P34xx · Auxiliary emission controls / P3420

P3420Cylinder 3 Deactivation/lntake Valve Control Circuit High

Q: What does code P3420 mean?

Cylinder 3 Deactivation/lntake Valve Control Circuit High. P3420 indicates that the powertrain control module (PCM) has detected an abnormally high voltage on the control circuit for the cylinder 3 deactivation or intake valve control solenoid. This circuit is used on engines with cylinder deactivation or variable valve timing to disable or adjust the intake valve for cylinder 3, and a high voltage reading typically means the circuit is open, shorted to power, or the solenoid has failed.

P3420 indicates that the powertrain control module (PCM) has detected an abnormally high voltage on the control circuit for the cylinder 3 deactivation or intake valve control solenoid. This circuit is used on engines with cylinder deactivation or variable valve timing to disable or adjust the intake valve for cylinder 3, and a high voltage reading typically means the circuit is open, shorted to power, or the solenoid has failed.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaAuxiliary emission controls

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Rough idle or misfire sensation, especially when the engine tries to enter cylinder deactivation mode
Reduced fuel economy due to the engine remaining in full-cylinder operation
A slight hesitation or stumble during light-throttle cruising when deactivation is commanded
In some cases, the engine may enter limp mode or disable cylinder deactivation entirely

Common causes, most likely first

Failed cylinder 3 deactivation solenoid or intake valve control solenoid (open internal coil)
Open circuit in the control wire between the PCM and the solenoid, such as a broken wire or corroded connector
Short to voltage on the control circuit, often from chafed wiring near hot or moving components
Poor electrical connection at the solenoid or PCM connector, including loose pins or water intrusion
PCM driver circuit failure, though this is less common than wiring or solenoid faults
Aftermarket electrical accessories improperly tapped into the circuit causing voltage spikes

How to diagnose and fix it

Connect a scan tool and verify P3420 is active, then check for any related codes that might indicate a different root cause
Inspect the cylinder 3 deactivation solenoid connector and wiring for corrosion, loose pins, or physical damage
Measure resistance across the solenoid coil and compare to the manufacturer's specification to check for an open circuit
With the key on and engine off, backprobe the control wire at the solenoid to check for voltage; a high voltage with the solenoid disconnected suggests a short to power
Check continuity of the control wire from the PCM to the solenoid to rule out an open circuit
If the circuit tests good, substitute a known-good solenoid or perform a functional test with a scan tool to confirm the solenoid responds to commands
If all external checks pass, diagnose the PCM driver circuit or replace the PCM only after confirming no other faults exist

What the high voltage reading really means

A high voltage code on a solenoid control circuit often indicates an open circuit rather than a short to power, because the PCM pulls the circuit low to actuate the solenoid and sees high voltage when the circuit is broken.
Many technicians replace the solenoid first, but a corroded connector or chafed wire a few inches away is a more frequent cause of this code on higher-mileage vehicles.
Cylinder deactivation solenoids can fail intermittently when hot, so a resistance check on a cold engine may pass even though the solenoid is faulty.
This code does not always mean the engine has a mechanical valve problem; the fault is electrical, and the engine may run normally with the solenoid disabled.
Aftermarket remote starters or alarm systems tapped into the wrong wire can backfeed voltage onto the control circuit and set this code without any component failure.

Can I keep driving with P3420?

You can usually continue driving with P3420 because the engine will default to full-cylinder operation and remain driveable, but avoid heavy towing or aggressive acceleration until the fault is repaired. If the check engine light begins flashing or the engine runs very rough, stop driving and have it diagnosed promptly.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.