Powertrain, shared range

P349D Cylinder 6 Deactivation/Intake Valve Performance

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

P349D indicates that cylinder 6 drew in and pushed out air during events in which it should have stayed sealed. The test logic rests on a simple effect: every intake stroke leaves a dip in manifold pressure, so a resting cylinder should leave none. Ford's patent US8667835B2 and Delphi's US7314034B1 describe tracking these pulses event by event. GM applies the idea to its L84 and L87 V8s with filtered manifold pressure, 22 failures out of 25, Type B. The older GM AFM V8s also switch off cylinder 6, but there faults surface through the bank code P3400. Likely causes are a lifter whose locking pins do not release, a sticking solenoid or poor oil. P3442 is the control-performance sibling, P0306 the misfire code of this cylinder.

Likely causes

Locking pins of the cylinder 6 lifters do not release

Oil solenoid of cylinder 6 sticking

Low oil level or degraded oil

Intake leak or MAP sensor fault distorting the pressure pulses

Symptoms

Check engine lamp on
Higher fuel use in light-load cruising
Ticking from the engine valley

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

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