Circuit/System Description
WARNING: This page is about a different car, the 2010 GMC Sierra, 2010 GMC Cab & Chassis Sierra, 2010 Chevrolet Silverado, and 2010 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The pressure switch manifold (PSM) is a multiple switch assembly made up of 3 normally open pressure switches and 1 normally closed pressure switch. Control main pressure is directed through an orifice to pressure switch 4 (PS4) and manual selector valve. When the selector lever is in park, neutral, or any forward position, the exhaust port is blocked and fluid pressure increases to the normally closed PS4. The transmission control module (TCM) monitors the PS4 to determine the position of the manual selector valve. The TCM provides a signal circuit to PS4. The low reference to the switches is provided through the metal base of the PSM which is connected to chassis ground through the transmission case.