Neutral Safety Switch: Testing and Inspection

Park/Neutral Position Switch Diagnosis






Circuit Description

The park neutral position (PNP) switch contacts are closed to ground when the transmission gear selector is placed in the Park and the Neutral positions, and open in Reverse and the Drive positions.

The powertrain control module (PCM) supplies ignition voltage, through a current limiting resistor, to the Park/Neutral signal circuit and senses a closed PNP switch when the voltage on the Park/Neutral signal circuit drops to less than 1 volt.

The PCM uses this signal as one of the inputs in order to control the following functions:

* Throttle angle at idle
* Fuel delivery at idle
* Inhibit the starter relay operation when the transmission is in gear (neutral start)

Diagnostic Aids

Important: The PCM will not energize the starter relay if the park/neutral signal circuit to the PCM is open or if the PNP switch is disconnected.


When the ignition switch is turned to the START (crank) position and the Park/Neutral signal circuit indicates Park/Neutral (grounded), the PCM will energize the starter relay even if the transmission gear selector is in a Drive or Reverse range.


If the neutral signal circuit indicates neutral (grounded), while in drive range, the EGR would be inoperative, resulting in possible detonation.

If the neutral signal circuit always indicates Reverse/Drive (open), a drop in the idle may exist when the gear selector is moved into Drive or Reverse range.

Test Description

The numbers below refer to the step numbers on the diagnostic table.
2. Checks for a closed switch to ground in the Park and the Neutral position.
3. Be sure scan indicates both positions, even while wiggling shifter in order to test for an intermittent switch in the Reverse and all of the Drive positions of the transmission gear selector.
5. This step determines if the problem is in the switch or the circuits.