P349B code meaning
Cylinder 4 Deactivation/Intake Valve Performance
Powertrain system Generic code P34xx codes Check engine light
What P349B means
P349B is set when cylinder 4 fails to shut its valves on command. On Mazda's 2.5 l Skyactiv-G with cylinder deactivation (CX-5 and Mazda6, 2018-2019), cylinders 1 and 4 can be switched off; service alerts SA-041/18 and SA-022/19 tie P349B, P3498, P3400, P0304 and P0340 to a rocker arm that fell out of place or broke. Technicians are told to check the oil change records as well, and Mazda handles such cases with a replacement engine. GM's L84 and L87 use the code for cylinder 4 with the same manifold pressure test as for the other seven cylinders, Type B. Circuit faults would be P3425, P3427 and P3428, the control-performance code P3426. Expect noise from the head, rough idle and weak pull.
P349B at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyWorkshop only
- Typical labor0.5 to 16 hours
- Clears after repairAfter a drive cycle
Symptoms of P349B
- Rough idle and misfire on cylinder 4 (P0304)
- Clatter or knocking from the valve cover area
- Lack of power
- Check engine lamp on
Common causes of P349B
- Most likelyRocker arm of cylinder 4 fallen out of place or broken (Mazda)
- PossibleLong oil change intervals or unsuitable oil
- PossibleDeactivation lifter of cylinder 4 stuck locked (GM DFM)
- Less likelyOil control solenoid of cylinder 4 faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Valve trainLifterCylinder deactivation solenoidEngine oil
What each part of P349B means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 3 | Mixed range: generic and manufacturer-specific codes. |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| 9B | The exact fault in that area. |
What to do next
- Note P349B and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P349B
What does P349B mean?
P349B means "Cylinder 4 Deactivation/Intake Valve Performance". P349B is set when cylinder 4 fails to shut its valves on command. It is a generic code, so it means the same on every make.
Is it safe to drive with P349B?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P349B fail an emissions test?
Yes, it can. P349B is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P349B to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 16 hours of work. This is a job for a workshop.
Will P349B clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.