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

Transmission control valve failure and rear-wheel lock-up (recall 24V-797)

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

Symptoms

momentary rear-wheel lock-up or a violent downshift at speed, often with a check-engine light and a reduced-power message
shudder, harsh or skipped shifts before the event; owners report repeat events after the recall visit

Root cause

GM recall 24V-797 (10/2024, 463,295 vehicles): on 2020-2022 Silverado/Sierra and 2021 Escalade/Tahoe/Suburban/Yukon with diesel engines the transmission control valve may fail and lock the rear wheels. Remedy: new transmission control module software that detects a failing valve, plus a special coverage to repair transmissions it flags. NHTSA: 120 of 1,190 VIN-confirmed 3.0 diesel complaints describe the lock-up or the valve body (another 87 other transmission complaints); 44 of the 120 come from MY2023 trucks, which the recall does not list - included here as complaint-documented, not recall-covered.

Diagnosis

check recall 24V-797 by VIN first - the software and the covered transmission repair are free
MY2023 trucks are outside the recall: record the event and codes and ask the dealer about any newer GM program before paying
on a test drive, make hard downshifts between 35 and 65 mph

Fixes

recall 24V-797 transmission control module software; transmission repair under GM special coverage when the software flags the valve ()

Prevalence

common