Circuit Description
WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The Transmission Control Module (TCM) uses input from the input and output speed sensors to determine gear ratios. The TCM then compares the known gear ratio to the calculated gear ratio for the current range.
This is a type "X" DTC.