Powertrain, shared range

P349B Cylinder 4 Deactivation/Intake Valve Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Rocker arm of cylinder 4 fallen out of place or broken (Mazda)
Long oil change intervals or unsuitable oil
Deactivation lifter of cylinder 4 stuck locked (GM DFM)
Oil control solenoid of cylinder 4 faulty

Symptoms

  • Rough idle and misfire on cylinder 4 (P0304)
  • Clatter or knocking from the valve cover area
  • Lack of power
  • Check engine lamp on

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€100–6,000
Time0–16 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

valve trainliftercylinder deactivation solenoidengine oil

Related codes

P3426P3425P3400P3498P349AP349CP0304P0340

References: static.nhtsa.gov, static.nhtsa.gov, gsi.ext.gm.com, law.cornell.edu.