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

Coolant flow control valve failure (active thermal management)

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

Symptoms

constant high-running radiator fan, fluctuating temperature, 'Engine Power Reduced' message
P1098 (and neighboring circuit codes); temperature spikes past 210F in traffic
some trucks fail repeatedly; GM Special Coverage N252508341 (09.2025) covers the valve only when onboard diagnostics confirm it as the root cause

Compare with the other causes of the same sign on this engine: loss of power, limp mode or derate (7 causes) · overheating or temperature creeping up

Root cause

The LM2's electronically-actuated coolant flow control valve (active grille/thermal management era hardware) sticks or fails; a second failure mode is harness/connector corrosion at the valve actuator rather than the valve itself. The platform's largest NHTSA cluster (192 of 1,190 VIN-confirmed diesel complaints, MY2021 peak of 93) - the SUV diesel debut year.

Diagnosis

P1098 + fan/temp behavior isolates the valve circuit; inspect the harness connector for corrosion before ordering the valve (forum-documented split)
check Special Coverage N252508341 eligibility by VIN before paying out of pocket (owner reports of inconsistent VIN coverage)

Fixes

replace the coolant flow control valve (check the special-coverage window first; the harness-connector corrosion variant is repair work on the valve circuit - no separate catalog part) ()

3.0L Duramax Engine Coolant Flow Control Valve (GM 24001355)

Prevalence

very-common

Parts for this repair run about $330: see them next to the other repairs on this engine in repair costs.