P3458Cylinder 8 Deactivation/Intake Valve Control Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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.
- What you may notice
- Check engine lamp on, sometimes going out again
- Shake or roughness in light-load cruising
- Misfire on cylinder 8 (P0308)
- Likely causes
- PossibleCylinder 8 deactivation lifter not unlocking or relocking
- PossibleOil pressure too low or oil aerated
- PossibleCylinder 8 solenoid valve sluggish or its screen blocked
- RareFalse entry after low voltage while cranking, fixed by ECM update (GM analogue 20-NA-204)
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €3,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.