01 Factors Affecting Start-Stop System Functionality in Vehicl… • 02 This Is Why Your Car’s Extended Warranty Is A Scam • 03 U0003, U0004, U0005, U0006, U0007, and U0008: High Speed CA… • 04 Who is at Fault When a Car Turns Right and a Bike Goes Stra… • 05 Why Does Car AC Only Work When Driving? Comprehensive Cause… • 06 Should I Press the Clutch Every Time I Need to Apply Brakes… • 07 C0040 and C0041: Right Front Wheel Speed Circuit Malfunction • 08 Lean vs. Rich: Which Engine Problem Should You Worry About … • 09 Kia Recalls Nearly Half a Million Tellurides Due to Potenti… • 10 V10 vs V8 Engine: Which One is Better? •

DTC codes / P34xx · Auxiliary emission controls / P349F

P349FCylinder 8 Deactivation/Intake Valve Performance

P349F indicates that the powertrain control module has detected a performance fault in the cylinder 8 deactivation or intake valve control system, meaning the engine cannot properly switch that cylinder between active and deactivated states. The computer monitors valve lift and response time and sets this code when the expected change does not occur within the calibrated window.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaAuxiliary emission controls

Symptoms you may notice

  • Illuminated check engine light, often with no other noticeable symptoms
  • Rough idle or misfire-like shaking, especially when the engine transitions between modes
  • Reduced fuel economy because the cylinder may remain active when it should deactivate
  • A slight hesitation or stumble during light-throttle cruising
  • Audible ticking or tapping from the valvetrain area on the affected bank
  • In rare cases, the engine may enter limp mode or limit power to protect the valvetrain

Common causes, most likely first

  1. Faulty oil control solenoid or its electrical connector for the cylinder deactivation system
  2. Sticking or clogged hydraulic lifter or rocker arm in the deactivation mechanism
  3. Low engine oil level or degraded oil that prevents proper hydraulic actuation
  4. Wiring damage, corrosion, or poor ground at the deactivation solenoid circuit
  5. Mechanical wear in the intake valve train, such as a worn cam lobe or collapsed lifter
  6. Failed valve deactivation pressure sensor or switch
  7. Internal PCM software calibration issue or faulty driver circuit

How to diagnose and fix it

  1. Check engine oil level and condition; top off or change oil if it is low or dirty
  2. Inspect the oil control solenoid connector and wiring for corrosion, looseness, or damage
  3. Use a scan tool to command the cylinder deactivation on and off while watching live data for response
  4. Perform a cylinder contribution or compression test to rule out mechanical valve train damage
  5. Test the oil control solenoid resistance and compare to specification; replace if out of range
  6. Check oil pressure at the deactivation gallery if accessible, and verify the solenoid screen is not clogged
  7. If electrical and hydraulic checks pass, inspect lifters and rocker arms for wear or sticking, and repair as needed

What most technicians overlook on P349F

  • A dirty or restricted oil control screen on the solenoid is a frequent culprit that does not always set a low oil pressure code.
  • The code can be set by a lazy oxygen sensor or misfire monitor interaction, so always check for pending misfire codes before condemning the deactivation hardware.
  • After replacing a solenoid or lifter, the PCM may need a relearn or adaptation reset before the code will clear permanently.
  • Intermittent wiring faults at the solenoid connector often appear only when the engine is hot, so wiggle-test the harness while monitoring live data.
  • Some vehicles use the same solenoid for multiple cylinders, so a failure can set codes for more than one cylinder even if only one is reported.

Can I keep driving with P349F?

You can usually drive the vehicle short distances at moderate speed, but avoid heavy acceleration or towing because the affected cylinder may not deactivate properly and could cause further valve train wear. If the engine runs rough or enters limp mode, stop driving and have it diagnosed promptly.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage