— GM 6L90 transmission failures seem to be over after General Motors released a technical service bulletin to dealers and a customer satisfaction program for vehicle owners.
The National Highway Traffic Safety Administration opened the investigation in September 2023 following complaints about GM 6L90 transmission failures.
All the General Motors 6L90 transmission failures occurred in 2016-2018 and 2021-2022 Chevrolet Express and GMC Savana cutaway vans used for school buses and ambulances. Drivers complained the vehicles lost all propulsion when shifting into DRIVE or REVERSE.
A stranded ambulance or school bus is never a good proposition, so NHTSA opened the probe to determine the cause of the failures.
GM says valve body separator plates had been machined out of tolerance between October 2016 to April 2017, and from February 2021 to April 2021. This results in excessive wear to the valve body check balls.
General Motors issued technical service bulletin (TSB 23-NA-142) to dealerships in September 2023 advising technicians to replace the forward check balls and separator plates.
Customer satisfaction program N232428780 was issued in February 2024 to notify school bus and ambulance fleets about the problems.
NHTSA also contacted multiple Chevrolet Express and GMC Savana cutaway van owners to verify there had been no more complaints.
Safety regulators have closed their investigation based on GM's actions.
