GM has found the root cause of the transmission problems experienced by some C8 Corvette owners that can result in a ‘Service Transmission’ message appearing on the Driver Information Center (DIC).
According to a recent post on the GM TechLink site, some 2020 to 2022 model year C8 Corvette owners may observe a ‘Service Transmission’ message on the DIC, along with an illuminated Check Engine light and a squealing sound immediately after starting the engine. Error codes may also be stored in the Engine Control Module (ECM) and Transmission Control Module (TCM) indicating there is a problem with these systems.
GM says that these problems are default actions of the vehicle when the TCM is in a defaulted state. When this happens, the TCM may not be properly controlling the pressure in the transmission line, resulting in the transmission operating at maximum line pressure. A permanent fix for this problem is not available at this time, although GM TechLink says the condition “should be resolved by allowing the vehicle to go through a complete sleep cycle (i.e., 15 minutes).” The site also suggests technicians “explain to customers that they can complete this process if they experience the condition again before a correction is available.”
GM pushed an over-the-air software update to certain C8 Corvette models last November to address a problem related to those vehicles’ TCM. The automaker also launched an investigation into certain Corvette C8 transmissions last year after receiving reports that some owners had experienced gasket failures. It does not appear as though this line pressure problem is related to either of those issues.
GM says permanent repair information for owners experiencing the line pressure problem described in this article “will be released when available.”