Automatic Transmission Fluid Pressure Manual Valve Position Switch

Fig 1: Automatic Transmission Fluid Pressure Manual Valve Position Switch

Courtesy of GENERAL MOTORS CORP.

The automatic transmission fluid pressure (TFP) manual valve position switch assembly is a gear range sensing device used by the PCM in order to sense which gear range has been selected by the vehicle operator. The TFP manual valve position switch assembly is located on the valve body, and consists of five pressure switches combined into one unit. The PCM applies system voltage to the TFP manual valve position switch assembly on three separate wires. These three circuits are either grounded or open, depending on which gear range has been selected, and on which combination of the five switches gave pressure applied to them.

When the vehicle is in PARK, with the key ON and the engine OFF, the normal state of the TFP manual valve position switch assembly will be DRIVE 2. When the key is ON and the engine is running, the normal state of the TFP manual valve position switch assembly is in PARK/NEUTRAL.

There are two possible combinations of the switches within the pressure switch manifold that do not represent an actual gear range. If the PCM detects either of these combinations, then a diagnostic trouble code (DTC) sets.

The PCM TFP DTC P1810 sets when the TFP switch indicates the following:

• An illegal gear range
• DRIVE4, DRIVE2 or REVERSE position before and after start-up
• PARK/NEUTRAL with a ratio greater than 1.05
• REVERSE with ratio indicating outside of REVERSE
• DRIVE4, DRIVE3, DRIVE2 or DRIVE1 with ratio indicating REVERSE

While DTC P1810 is present, the PCM assumes DRIVE4 for shift pattern, sets line pressure to maximum, freezes shift adapts, and forces TCC ON with 4th gear commanded.