Transmission Position Sensor/Switch: Testing and Inspection

Circuit Description
The Park/Neutral Position (PNP) Switch contacts are a part of the Neutral Start Switch Assembly. They are closed to ground in park or neutral and open in drive ranges.

The Engine Control Module (ECM) supplies voltage through a current limiting resistor to BLU/PNK wire and senses a closed switch when the voltage on BLU/PNK wire drops to less than one volt. The ECM uses the PNP signal as one of the inputs to control idle air, Vehicle Speed Sensor diagnostics, and Exhaust Gas Recirculation.

If BLU/PNK wire indicates PNP (grounded), while in drive range, the ECM would be inoperative, resulting in possible detonation. If BLU/PNK wire indicates drive (open), a dip in the idle may exist when the Gear Selector is moved into drive range.




Test Description
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Checks for a closed Switch to ground in park position. Different makes of "Scan Tools" will read PNP differently. Refer to Tool operators manual for type of display used for a specific tool.
2. To gain access to the wiring for the Diode, it will be necessary to remove the lower cover of the underhood Fuse/Relay Center.