Broken, chafed, or corroded wiring in the exhaust valve control circuit for cylinder 4; Failed exhaust valve control solenoid or actuator (open coil or stuck armature); Loose, corroded, or disconnected electrical connector at the solenoid or PCM; Open circuit inside the PCM driver for that specific cylinder's exhaust valve control; Blown fuse or relay supplying power to the exhaust valve control circuit (if applicable); Internal mechanical failure of the exhaust valve or valvetrain preventing proper solenoid operation

DTC codes / P34xx · Auxiliary emission controls / P3429

P3429Cylinder 4 Exhaust Valve Control Circuit/Open

Q: What does code P3429 mean?

Cylinder 4 Exhaust Valve Control Circuit/Open. P3429 indicates that the powertrain control module (PCM) has detected an open circuit or excessive resistance in the electrical path controlling the exhaust valve for cylinder 4. This circuit typically operates a variable valve timing or cylinder deactivation solenoid that adjusts exhaust valve timing or disables the valve, and the PCM monitors current flow to confirm the circuit is intact. An open circuit means the PCM cannot command the valve actuator, which may affect engine breathing, emissions, or fuel economy.

P3429 indicates that the powertrain control module (PCM) has detected an open circuit or excessive resistance in the electrical path controlling the exhaust valve for cylinder 4. This circuit typically operates a variable valve timing or cylinder deactivation solenoid that adjusts exhaust valve timing or disables the valve, and the PCM monitors current flow to confirm the circuit is intact. An open circuit means the PCM cannot command the valve actuator, which may affect engine breathing, emissions, or fuel economy.

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-like shudder, especially when the engine is cold or under light load
Reduced engine power or sluggish acceleration due to improper exhaust valve operation
Poor fuel economy as the engine cannot optimize valve timing or deactivation
Intermittent engine stumble or hesitation if the open circuit is temperature or vibration sensitive
Failed emissions test due to increased exhaust emissions from improper valve control

Common causes, most likely first

Broken, chafed, or corroded wiring in the exhaust valve control circuit for cylinder 4
Failed exhaust valve control solenoid or actuator (open coil or stuck armature)
Loose, corroded, or disconnected electrical connector at the solenoid or PCM
Open circuit inside the PCM driver for that specific cylinder's exhaust valve control
Blown fuse or relay supplying power to the exhaust valve control circuit (if applicable)
Internal mechanical failure of the exhaust valve or valvetrain preventing proper solenoid operation

How to diagnose and fix it

Connect a scan tool and verify P3429 is current, then check for related codes and freeze-frame data
Visually inspect the exhaust valve control solenoid connector and wiring for damage, corrosion, or looseness
Measure resistance of the exhaust valve control solenoid with a multimeter and compare to manufacturer specification
Perform a voltage drop test on the power and ground sides of the circuit while commanding the solenoid on with a scan tool
Check for continuity and short-to-ground on the control wire between the PCM and solenoid, repairing any open or chafed section
If wiring and solenoid test good, substitute a known-good solenoid or perform a bidirectional actuator test to confirm PCM driver operation
Clear codes and road test to verify the repair, monitoring live data for proper exhaust valve control command and feedback

What the open circuit really means

An open circuit code does not always mean the solenoid has failed; a poor ground or corroded connector pin can set the same code without any component fault.
Cylinder-specific exhaust valve control circuits are often part of a multi-cylinder harness, so a single chafed wire near a heat source can affect only one cylinder and mimic a mechanical valve problem.
Some vehicles use the exhaust valve control solenoid for cylinder deactivation, and a failure may cause the engine to stay in full-displacement mode, leading to poor fuel economy that the driver notices before the warning light.
A scan tool bidirectional test that commands the solenoid on and off is the quickest way to confirm whether the PCM driver or the circuit is at fault, avoiding unnecessary PCM replacement.
Intermittent P3429 codes that appear only when cold or after a bump are classic signs of a wire break inside the insulation that a simple resistance check at room temperature will miss.

Can I keep driving with P3429?

The vehicle is generally safe to drive short distances to a repair shop, but avoid heavy acceleration, towing, or long highway trips because improper exhaust valve operation can cause misfires, overheating, or catalytic converter damage over time. If the check engine light flashes or the engine runs very rough, stop driving and have it towed.

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.