Trans Hot...Idle Engine
WARNING: This page is about a different car, the 1999 GMC Sierra and 1999 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The transmission fluid temperature is sent to the cluster as a class 2 serial data value from the PCM/VCM. The cluster turns on the TRANS HOT...IDLE ENGINE message based on the trans fluid temperature. If the transmission fluid temperature is greater than 275°F (135°C) will be added to the message center and removed when the transmission fluid temperature drops below 270°F (132°C).