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

Turbo and boost-path faults (coolant line, charge air)

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

Symptoms

underboost/overboost codes (P0299 family), smoke, power loss
coolant loss traced to the hard coolant line to the turbo (community-documented)

Compare with the other causes of the same sign on this engine: loss of power, limp mode or derate (7 causes) · losing coolant (2 causes)

Root cause

Thin NHTSA record (9 VIN-confirmed complaints) but a consistent community thread pattern: the turbo's hard coolant line weeps, and boost-path leaks (charge-air piping) mimic turbo failure. The TSB MC-10165111 coolant-circuit document overlaps the EGR/turbo cooling path.

Diagnosis

smoke-test the boost path before condemning the turbo (underboost is often a pipe/clamp)
check the turbo coolant line when coolant loss coincides with turbo-area residue

Fixes

replace the turbocharger (or have it rebuilt) when the wheel/housing is the fault; the diesel coolant-line rows are not carded in the dealer catalog (the 2.7L gas rows are - do not cross-order) ()

turbocharger - more than one option: 3.0L Duramax Turbocharger (GM 40009138), 3.0L Duramax Turbo Wastegate Actuator Kit (GM 12716475)

Prevalence

occasional