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, the torque converter clutch (TCC) pressure control solenoid, and the pressure control solenoid 1 (PCS1), through a separate solid state device called high side driver 1 (HSD1). The TCM also provides B+ to the pressure control solenoid 2 (PCS2) and shift solenoids (SS) 1, 2, and 3 through a separate solid state device called high side driver 2 (HSD2). The TCM uses low side drivers to control the solenoids.