P349BCylinder 4 Deactivation/Intake Valve Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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.
- What you may notice
- Rough idle and misfire on cylinder 4 (P0304)
- Clatter or knocking from the valve cover area
- Lack of power
- Check engine lamp on
- Likely causes
- 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)
- RareOil control solenoid of cylinder 4 faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €100 – €6,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.