This bulletin applies to 2010-2012 Buick LaCrosse and 2008-2012 Enclave models. The customer may comment that the DIC (driver information center) displays a “Transmission Hot – Idle Engine” message. The technician may find DTC P0218 or P0634 stored.
The most likely cause of transmission over-temperature is an over-filled transmission fluid level. Inspect the transmission fluid level when the TFT (transmission fluid temperature) is between 180 and 200 degrees Fahrenheit. The fluid level rises as temperature increases, so it’s important to ensure that the transmission fluid temperature is within range.
Test drive the vehicle and try to duplicate the concern. Monitor the ECT, TFT and TCM temperature throughout the test drive. Review freeze frame data and record ECT, TFT and TCM temperature. If the freeze frame data and/or the test drive show that the ECT was running higher than normal, proceed to diagnose any potential engine concerns before investigating the transmission. If the ECT is running normal and only the transmission is overheating, continue to diagnose the transmission.
Carefully inspect the transmission fluid level following the proper transmission fluid level and condition check procedure in the service manual. An overfilled transmission is the primary cause of overheat concerns in 6T70 and 6T75 transmissions.
Check for signs of an internal transmission concern by first pulling a sample of the transmission fluid through the drain plug.
Also, while test driving, monitor for any gear shifting issues that may indicate an internal concern. Diagnose any other transmission diagnostic codes prior to diagnosing the temperature issue. Check for a restriction in the transmission cooler circuit. Check for proper transmission cooler circuit flow using DT-45096 and following the transmission fluid cooler flushing and flow check procedure in the service manual.
Check (if possible) the repair history of the vehicle for any prior transmission repairs that may have generated debris that could restrict cooler flow.