Gear Switches

WARNING: This page is about a different car, the 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, 2003 Chevrolet Monte Carlo, and 2003 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.

The automatic Transmission Fluid Pressure (TFP) manual valve position switch assembly is attached to the control valve body. This assembly contains six fluid pressure switches and the automatic transmission fluid temperature sensor. Five of the fluid pressure switches are normally-open. These are used to indicate the position of the manual valve. The PCM uses this information to control line pressure, TCC apply and release and shift solenoid operation.

The release pressure switch is used as a diagnostic tool to confirm that the TCC is actually OFF when it has been commanded OFF by the PCM. This switch is normally-closed. Each fluid pressure switch produces either an open or a ground to the PCM depending on the presence of fluid pressure at the switches. The sequence of open and closed switches produces a combination of voltage readings. The PCM monitors these readings. The PCM measures TFP manual valve position switch signal voltage from each pin to ground and compares the voltage to a TFP manual valve position switch combination table stored in the PCM memory. If the PCM does not recognize the switch sequence, a diagnostic code will be set as a result. A diagnostic code may also set if the TFP manual valve position switch sequence indicates a gear range selection that conflicts with other sensory inputs to the PCM.