As Car Complaints reports, the investigation is looking specifically at cutaway Chevy Express and GMC Savana models equipped with the GM Hydra-Matic 6L90 MYD transmission, a six-speed, fuel-saving, electronically controlled automatic transmission for RWD and AWD.
Some evidence is pointing to the possibility that the 6L90 MYD transmission may cause the affected Chevy Express and GMC Savana units to lose power when the transmission is first shifting into “Drive” or “Reverse,” preventing the vehicle from moving.
All affected units are in the cutaway configuration, with Express units from the 2010 through 2018 and 2021 through 2022 model-year ranges. The Chevy Express and GMC Savana cutaway vans from the 2019 and 2020 appear to be unaffected.
GM conducted its own investigation of the issue at the behest of safety authorities and confirmed a defect in two batches of valve body separator plates that were improperly machined during manufacture. The plates wear out the plastic valve body check balls, causing a loss of propulsion.
The NHTSA launched the investigation in part because the Chevy Express and GMC Savana cutaway vans in question are used for ambulances and school buses. GM confirmed to the NHTSA that 1,961 of the vans with the possibly defective 6L90 MYD transmission were completed as small school buses and 89 are in use as ambulances.
Transmission failure in an ambulance, Car Complaints notes, could cause the vehicle to become immobilized while attempting to carry a badly injured or seriously ill person in need of immediate treatment. In the case of cutaways built as small school buses, losing motive power could strand a bus full of children in a dangerous spot, such as on a highway shoulder where it might be struck by other traffic.
GM recently announced the removal of the MYD transmission from several configurations of its 2024 light commercial vans. For both the 2024 Chevy Express and the 2024 GMC Savana, the naturally aspirated 6.6L V8 L8T gasoline engine rated at 401 horsepower and 464 pound-feet of torque – and equipped as standard on 3500 and 4500 series cutaways – will henceforth use the 8-speed heavy-duty automatic transmission (RPO code N8X) instead of the 6-speed MYD transmission.