02/07/2020
IMPORTANT SERVICE BULLETIN ON 2016 - 2020 GM REAR WHEEL DRIVE VEHICLES
We just performed a repair on a Chev Silverado with a 6.2L engine and an 8L90 transmission by replacing the internal transmission wiring harness. The customer told us that the check engine light would come on and the transmission would suddenly downshift to 3rd gear. This isn't so dramatic around town, but if the transmission downshifts to 3rd gear on the freeway, that could be frightening. GM put out a Technical Service Bulletin on 1/17/20 which generally includes 8L45 and 8L90 Transmissions produced from 2016 thru 2020. Models affected are Cadillac ATS, CT4, CT6, CTS, Escalade and Chev Camaro, Colorado, Corvette, Express, Silverado and GMC Canyon, Savana, Sierras. This is not a recall but if you have any of these vehicles and have had transmission shifting issues you should contact your dealer if it is still under Powertrain Warranty or Aamco if it is no longer under warranty.