Failure mode - Duramax 6.6L V8 Turbo Diesel (GM HD, LML 2011-2016; LGH vans 2011-2016)

Glow plug / control module cold-start service (LML)

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

Symptoms

hard starts only when cold; glow-plug circuit codes (often bank-specific)
control-module faults after plug replacement without module check

Compare with the other causes of the same sign on this engine: hard start, long crank or no-start (3 causes)

Root cause

Glow plugs fail open with age (often several on one bank) and the control module's drivers fail with or without plug faults; extended cranking on a marginal fuel system compounds the cold-start complaint.

Diagnosis

measure glow-plug resistance per plug; a failed module often kills a bank, not one plug
check module fuses/harness before replacing plugs individually

Fixes

replace failed glow plugs and/or the control module (couples with the CP4-era advice: minimize extended cranking on a weak-fuel system) ()

Duramax LML Glow Plug (OEM)
glow-plug-control-module - more than one option: Duramax LML Glow Plug Control Module 2011-2012 (OEM), Duramax LML Glow Plug Control Module 2013-2016 (OEM)

Prevalence

occasional

Parts for this repair run about $170-$280: see them next to the other repairs on this engine in repair costs.