Transmission Position Sensor/Switch: Testing and Inspection

Chart C-1A:

Park/Neutral Switch 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.

The ECM supplies ignition voltage through a pull-up resistor to CKT 434 and senses a closed switch when the voltage on CKT 434 drops to less than one volt. The ECM uses the PNP signal as one of the inputs to control:

^ Idle air control.
^ VSS diagnostics.
^ EGR.

If CKT 434 indicates PNP (grounded), while in drive range, the EGR would be inoperative, resulting in possible detonation. If CKT 434 indicates drive (open) a drop in the idle may occur 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 P/N 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 scan tool indicates drive, even while wiggling shifter, to test for an intermittent or misadjusted switch in drive range.