<ul> <li><b>Engine Light ON (or Service Engine Soon Warning Light)</b>: The illumination of the engine light indicates a detected issue with the exhaust valve control circuit for cylinder 12. This could be due to a malfunctioning valve control solenoid, wiring issues, or a faulty PCM (Powertrain Control Module).</li> <li><b>Reduced Engine Performance</b>: The vehicle may experience reduced power and performance due to improper exhaust valve operation, which can affect engine efficiency and combustion.</li> <li><b>Rough Idling</b>: The engine may idle roughly or inconsistently, as the exhaust valve for cylinder 12 may not be operating correctly, leading to imbalanced engine operation.</li> <li><b>Increased Emissions</b>: Faulty exhaust valve control can lead to incomplete combustion, resulting in higher emissions and potentially failing emissions tests.</li> </ul>

<ul><li>Low oil pressure can lead to insufficient lubrication and improper valve operation.</li><li>Restricted oil passage may prevent adequate oil flow to the exhaust valve control circuit.</li><li>Engine mechanical condition issues can affect the performance of the exhaust valve control circuit.</li><li>A faulty Cylinder Deactivation Solenoid can disrupt the control of the exhaust valve.</li><li>An open or shorted Cylinder Deactivation Solenoid harness can cause electrical failures in the circuit.</li><li>Poor electrical connection in the Cylinder Deactivation Solenoid circuit can lead to intermittent or failed valve control.</li></ul>

<ul> <li><b>Research Technical Service Bulletins (TSBs)</b>: Research TSBs for the specific vehicle by year, model, and engine to identify any known fixes for this issue.</li> <li><b>Check Engine Oil Condition</b>: Verify the engine oil is at the appropriate level and in good condition. Low or dirty oil can affect the variable valve timing system.</li> <li><b>Locate Cylinder 12 Exhaust Valve Control Circuit Components</b>: Identify and locate all components associated with the cylinder 12 exhaust valve control circuit, including the variable valve timing solenoid, switches, fault indicators, and the ECM.</li> <li><b>Perform Visual Inspection</b>: Inspect the associated wiring for defects such as scraping, rubbing, bare wires, or burn spots. Check connectors and connections for security, corrosion, and damaged pins.</li> <li><b>Check Variable Valve Timing Solenoid</b>: Test the variable valve timing solenoid for proper operation. Replace if faulty.</li> <li><b>Clean Corrosion from Connectors</b>: Clean any corrosion found on connectors to ensure proper electrical contact.</li> <li><b>Repair or Replace Faulty Wiring</b>: Repair or replace any damaged wiring found during the visual inspection.</li> <li><b>Clear Blocked Oil Passages</b>: Ensure that oil passages are clear and not blocked, as this can affect the performance of the variable valve timing system.</li> <li><b>Flash or Replace ECM</b>: If all other components are functioning correctly, consider flashing or replacing the ECM as a last resort.</li> <li><b>Clear DTC and Test Drive</b>: Clear the DTC code and perform a test drive to ensure the issue has been resolved.</li></ul>

<p>The DTC code P3494 indicates a performance issue in the Cylinder 12 Exhaust Valve Control Circuit. This is a critical issue as it can lead to severe engine performance problems, including misfires, reduced power, and potential engine damage.</p><ul><li><b>Immediate Actions:</b> Inspect the exhaust valve control circuit for faults.</li><li>Check wiring and connections for damage or corrosion.</li><li>Test the exhaust valve actuator for proper operation.</li></ul><p>Delaying repair can result in significant engine damage and costly repairs.</p>