Transaxle Pressure Switch
The transaxle pressure switch contains five normally open pressure switch assemblies, which are used to indicate transmission manual valve range through use of Binary code. Each switch produces either an open or a ground for three PCM/TCM signal lines, depending on which switches have pressure applied to them. The transaxle pressure switch is attached to valve body. See Figure . The sequence of which switches are open and which switches are closed will be used by PCM/TCM to determine actual manual valve position (except park/neutral). This input is used for line pressure, TCC and shift solenoid control.
The PCM uses transaxle pressure switch status for idle speed control, transaxle shift control and ignition control. A faulty transaxle pressure switch will cause various transaxle and engine driveability conditions and should set a PCM Trouble Code.
To monitor TPS operation, PCM/TCM compares voltage values it sees to a TPS combination chart stored in its memory. If PCM/TCM does not recognize TPS switch sequence (voltage sequence) for range selected, a Code 028 will result.
For a given range, TPS signal voltage can be measured from each pin to ground and compared to combination chart. See Fig 1 . On 8-way transaxle connector, pin A is "mode A", pin B is "mode B", and pin H is "Mode C". When checking for continuity transaxle harness remains connected, and wires must be probed. (12 = 12 volts, 0 = Grounded)