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/TCM in order to sense the gear range that has been selected by the vehicle operator. The TFP manual valve position switch assembly is located on the valve body, and consists of 5 pressure switches combined into 1 unit. The PCM/TCM applies system voltage to the TFP manual valve position switch assembly on 3 separate wires. These 3 circuits are either grounded or open, depending on the gear range that has been selected, and the combination of the 5 switches that 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 is DRIVE 2. When the key is ON and the engine is running, the normal state of the TFP manual valve position switch assembly is PARK/NEUTRAL.

There are 2 possible combinations of the switches within the pressure switch manifold that do not represent an actual gear range. If the PCM/TCM detects either of these combinations, a DTC sets.

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

• 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/TCM assumes DRIVE4 for shift pattern, sets line pressure to maximum, freezes shift adapts, and forces the TCC ON with 4th gear commanded.