Powertrain, shared range

P349C Cylinder 5 Deactivation/Intake Valve Performance

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

P349C means that cylinder 5 stayed active although the engine computer had requested a skip. GM documents it for its Dynamic Fuel Management V8s (L84 with 5.3 l, L87 with 6.2 l), where every cylinder may be skipped; the classic AFM V8s rest only cylinders 1, 7, 6 and 4. Detection compares filtered manifold pressure with a deactivation threshold, and a Type B code follows after 22 failures out of 25. For 2019 Silverado and Sierra trucks, GM's PIP5584 blames the lifter oil solenoid of the affected cylinder: replace it and inspect the remaining solenoids for a pole piece that stands proud of the surface. Wiring faults for cylinder 5 appear as P3433, P3435 and P3436. The driver sees the lamp and pays with higher fuel use.

Likely causes

Lifter oil solenoid of cylinder 5 faulty, pole piece protruding

Lifters of cylinder 5 do not unlock

Dirt in the oil blocking the solenoid or lifter bores

Symptoms

Check engine lamp on
Engine no longer skips cylinders, fuel use rises
Vibration at light load

Repair estimate

DifficultyHardWorkshop job

Parts and labour€100–4,500

Time0–14 h

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

Parts involved

cylinder deactivation solenoidliftervalve trainengine oil

References: gsi.ext.gm.com, static.nhtsa.gov, static.nhtsa.gov.