Powertrain, shared range

P349A Cylinder 3 Deactivation/Intake Valve Performance

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

P349A states that cylinder 3 kept its valves working while the engine computer had switched it off. GM picks this up on its L84 and L87 V8s through manifold pressure that stays too high during the skipped strokes, Type B after 22 failed checks out of 25. Not every stored P349A means a worn lifter. For the 2021 Tahoe, Suburban, Yukon and Escalade, GM explains (PIP5731, later bulletin 20-NA-204) that a voltage dip while cranking could make the ECM drop the deactivation outputs for one trip and log this code in history without a real defect; the cure is new ECM software and a road test with a warm engine at 30 to 45 mph. If it returns, the lifters and the solenoid of cylinder 3 need checking. P3418 covers the control side.

Likely causes

Voltage dip at cranking disabled the outputs, ECM software outdated

Deactivation lifter of cylinder 3 does not unlock

Lifter oil solenoid of cylinder 3 sticking

Low or aged oil slowing the switching

Symptoms

Code stored in history with no noticeable concern
Check engine lamp on if the fault is real
Ticking noise or higher fuel use

Repair estimate

DifficultyHardWorkshop job

Parts and labour€0–4,500

Time0–14 h

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

Parts involved

liftervalve traincylinder deactivation solenoidecm

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