Powertrain, shared range

P349F Cylinder 8 Deactivation/Intake Valve Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P349F reports that cylinder 8 failed to go quiet when commanded. California's OBD rule requires makers to analyse every plausible hydraulic or mechanical failure of variable valve systems and mentions, among its examples, a lift-mechanism pin of one cylinder that will not shift; codes like this one follow from that duty. GM implements it for cylinder 8 on its L84 and L87 DFM V8s: filtered manifold pressure above the deactivation threshold in 22 out of 25 chances, rated Type B, so the lamp lights on the second faulty trip. GM's LT2 and LTA engines also rest cylinder 8, but no public GM table assigns P349F to them. Typical causes are a lifter stuck in its locked state, a failing oil solenoid or sludge. P3458 is the control-side code, P0308 the misfire code.

Likely causes

Lifter of cylinder 8 stuck in its locked state
Weak or sticking oil solenoid of cylinder 8
Sludge or debris in the lifter oil passages
Stored after a voltage dip at cranking, ECM software update needed

Symptoms

  • Check engine lamp on after two trips
  • Engine stays on all cylinders, fuel use rises
  • Ticking noise at idle

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

liftervalve traincylinder deactivation solenoidengine oil

Related codes

P3458P3457P349EP34A0P3400P0308

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