Circuit/System Description
WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The transmission control module (TCM) provides B+ to the modulated main (MOD MAIN) pressure control solenoid, torque converter clutch (TCC) pressure control solenoid and pressure control solenoid 1 (PCS1) through a separate solid state device called high side driver 1 (HSD1). The TCM uses low side drivers to control the solenoids.