Failure mode - GM 3.0L Duramax LM2/LZ0 I6 (2020+)

Extended crank / long-crank no-start (air intrusion, check valve, cam wheel)

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

Symptoms

after sitting 2-3 days the engine cranks long before starting; a key-on prime cycle before cranking helps
long cranking right after a fuel filter change (air trapped in the system)
worst case: crank-but-no-start until the system re-primes

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

Root cause

Air intrusion / loss of fuel rail prime: forum-and-dealer-documented culprits are a weak check valve in the low-pressure side (lift pump), air intrusion at filter housings (O-ring seating), and a reported bent/warped camshaft wheel confusing the position sensor at start. 28 VIN-confirmed NHTSA complaints (long-crank/no-start family); strong community thread record.

Diagnosis

split by trigger: sits-2-days = low-pressure prime loss (check valve/lift pump); after-filter-change = trapped air (reseat the housing, O-ring, key-on prime cycles)
verify fuel filter seating and water-in-fuel service before deeper diagnostics

Fixes

replace the fuel filter with the housing fully seated (trapped-air prevention) ()

fuel-filter - more than one option: 3.0L Duramax Fuel Filter / Water Separator Assembly (GM 13543066), 3.0L Duramax Fuel Filter Kit (GM 13539108)

address the low-pressure side: lift pump / check-valve replacement where prime is lost overnight ()

3.0L Duramax Drop-In Fuel System / Lift Pump (FASS, 2019-2026 GM 3.0 LM2/LZ0)

Prevalence

common

Parts for this repair run about $50-$550: see them next to the other repairs on this engine in repair costs.