Transmission Fluid Pressure Manual Valve Position Switch
WARNING: This page is about a different car, the 2003 Buick Regal and 2003 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
The Transmission Fluid Pressure (TFP) manual valve position switch is attached to the valve body and consists of one fluid pressure switch that monitors TCC release pressure. See Figure and Fig 1 . This switch is used as a diagnostic tool to confirm that the TCC is actually OFF when it has been commanded OFF by the PCM.
The TCC release switch is a normally-closed pressure switch. A normally-closed switch allows current to flow from the positive contact through the switch to ground when no fluid is present. Fluid pressure moves the diaphragm to disconnect the positive and ground contacts, opening the switch and stopping current flow. This change in switch status electronically signals the PCM that the TCC is released.