Transmission Position Sensor/Switch: Testing and Inspection

Chart C-1A - Park/Neutral Position (PNP) Switch Diagnosis (Auto Trans Only):

Park/Neutral Position (PNP) Switch Wiring Circuit:

Circuit Description:

The Park/Neutral Position (PNP) switch contacts are a part of the neutral start switch and are closed to ground in park or neutral, and open in drive ranges and reverse.

The Engine Control Module (ECM) supplies ignition voltage through a current limiting resistor to CKT 434 and senses a closed switch when the voltage on CKT 434 drops to less than 1 volt.
The ECM uses the PNP signal as one of the inputs to control:
^ Idle Air Control (IAC) valve.
^ DTC 24 VSS diagnostics.
If CKT 434 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 display PNP differently. Refer to "Tool Operator's" manual for type of display used for a specific tool.
2. Checks for an open switch in drive range.
3. Be sure Tech 1 scan tool indicates drive, even while wiggling shifter, to test for an intermittent or misadjusted switch in drive range.