Powertrain, shared range

P3458 Cylinder 8 Deactivation/Intake Valve Control Performance

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

P3458 describes a cylinder 8 that does not deactivate or reactivate as commanded although its control circuit is electrically fine. No manufacturer documents this code publicly. GM, the only maker with published cylinder 8 deactivation codes, files this failure under P349F on the L84: during a commanded skip, filtered manifold pressure stays above a threshold, which means the intake and exhaust valves kept working; the test runs with air charge above 120 mg and MAP/BARO between 0.30 and 0.95, and 22 failures in 25 opportunities give a Type B code. Bulletin 20-NA-204 adds that on 2021 full-size SUVs with L84 and L87 a voltage dip during cranking can set P349F without any hardware fault. Electrical faults are P3457, P3459 and P3460.

Likely causes

Cylinder 8 deactivation lifter not unlocking or relocking

Oil pressure too low or oil aerated

Cylinder 8 solenoid valve sluggish or its screen blocked

False entry after low voltage while cranking, fixed by ECM update (GM analogue 20-NA-204)

Symptoms

Check engine lamp on, sometimes going out again
Shake or roughness in light-load cruising
Misfire on cylinder 8 (P0308)

Repair estimate

DifficultyHardWorkshop job

Parts and labour€100–3,500

Time0–12 h

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

Parts involved

cylinder deactivation solenoidlifterengine oil

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