Circuit Description
WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Vehicles currently using the 8.1 liter gas engine use a 3 wire system to communicate engine torque data/requests between the engine control module (ECM) and the transmission control module (TCM).
DTC P1688 is a type B DTC.