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

In-tank lift pump / low-pressure fuel delivery stalls

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

Symptoms

random loss of motive power / stalling at speed with no warning light (NHTSA VOQ 'FUEL SYSTEM, DIESEL' records)
fuel pump control module fault codes reported (one owner: P129F)

Compare with the other causes of the same sign on this engine: stalls or dies while driving · loss of power, limp mode or derate (4 causes)

Root cause

The electric in-tank lift pump and its control/driver side can fail and starve the high-pressure system; VOQ carries stall/loss-of-power complaints filed under diesel fuel-system components. The specific failure split (pump vs driver module vs wiring) is not settled in the open record - no lift-pump-specific VOQ language, community support exists (aftermarket lift-pump kits are an active L5P category).

Diagnosis

log low-pressure fuel supply during a stall event; distinguish electrical (driver/harness) from pump wear
check for stored fuel-pump control DTCs (e.g. P129F reported by an owner)

Fixes

replace the in-tank lift pump module or the failed control/driver side; aftermarket external lift pumps are an upgrade path ()

Prevalence

occasional