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.

Main Modulation/Line Pressure Control (MAIN MOD) Solenoid is a normally closed (N/C) solenoid that regulates transmission line pressure. This solenoid is used to reduce line pressure when the vehicle is not moving with engine at idle, thus decreasing engine load and also improving cooler flow. The transmission control module (TCM) commands the MAIN MOD solenoid ON when specific transmission and engine conditions are met. When the MAIN MOD solenoid is commanded ON, control main pressure is routed to the main regulator valve lowering the line pressure.

The TCM provides B+ to the MAIN MOD 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 a low side driver to switch the MAIN MOD solenoid ON and OFF.