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

Bosch CP4.2 high-pressure pump failure and fuel-system contamination

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

Symptoms

sudden loss of power / rough running, then a no-start as rail pressure collapses
metal shavings in the fuel filter housing; the CP4's internal cam/c-roller wears through and sends debris down the high-pressure lines into the rails and injectors
repair bills owners report at $7,000-$17,000 (NHTSA complaints 2016-2025): the documented outcome is a full tank-to-injector fuel system replacement, not just a pump

Compare with the other causes of the same sign on this engine: hard start, long crank or no-start (3 causes) · loss of power, limp mode or derate (4 causes) · misfire, rough idle, hesitation or surging (3 causes) · metal in the fuel filter or oil

Root cause

The Bosch CP4.2's roller/cam-lifter interface is under-lubricated by design on low-sulfur fuel; wear eventually punches through and floods the high-pressure circuit with metal. Downstream, only full replacement of everything the debris touched restores the system - this is why the repair is infamous for exceeding the cost of many trucks. GM dropped the CP4 after the LML - the L5P's Denso HP4 does not share this failure pattern (the L5P record states the converse). ULSD's low lubricity is the standing risk factor; extended cranking after a running failure spreads debris further.

Diagnosis

cut open the fuel filter first: metal particles = CP4 cascade, stop cranking
quantify rail pressure complaints (crank-no-start after a running event is the classic signature) before spending on injectors
any pump replacement on a contaminated system must be paired with full-system decontamination - lines, rails, injectors, tank

Fixes

full fuel-system decontamination (tank, lines, CP4 replacement, rails, injectors); the only reliable repair once metal is downstream ()

prevention: on-schedule fuel filters, quality fuel, lubricity additive; CP3-conversion and CP4 bypass kits exist in the aftermarket (recorded where catalog-verified) ()

Prevalence

very-common

Parts for this repair run about $2,350-$5,000: see them next to the other repairs on this engine in repair costs.