Failure mode - Duramax 6.6L V8 Turbo Diesel (GM HD, L5P 2017+ generation)

Glow plug failures - fragile ceramic tips (R&R hazard)

Reliability tier: aggregated - verify before ordering, see /disclosure/

Symptoms

extended cranking / rough cold idle on cold mornings
catastrophic engine damage after a DIY glow plug R&R breaks a ceramic tip into the cylinder - the documented hazard

Compare with the other causes of the same sign on this engine: hard start, long crank or no-start (2 causes) · misfire, rough idle, hesitation or surging (4 causes)

Root cause

L5P glow plugs use delicate ceramic tips that crack under side load during removal/installation; the system is controlled by the GPCM and ECM, and a replacement glow plug requires a learn procedure. VOQ is nearly silent (1 word-boundary hit) - this record rests on community documentation.

Diagnosis

test glow plug resistance/control via the GPCM before pulling plugs; avoid side-loading the ceramic tip on removal
after any glow plug replacement, run the glow plug learn procedure per service documentation

Fixes

replace failed glow plugs with the correct ceramic-tip parts and perform the learn procedure; replace the GPCM if control-side faults are present ()

Prevalence

occasional