Chart C-1A, Park/Neutral Switch - Light Trucks & Vans: Notes

Fig 1: Chart C-1A, Park/Neutral Switch Circuit Diagram (Lt. Trucks & Vans)

Courtesy of GENERAL MOTORS CORP.

The Park/Neutral switch contacts are closed to ground in Park or Neutral, and open in all Drive ranges. The ECM supplies ignition voltage, through a current limiting resistor, to circuit No. 434. The ECM senses a closed switch when voltage on circuit No. 434 drops to less than one volt. The ECM uses Park/Neutral signal as one of the inputs to control idle air, VSS diagnostics, and EGR flow.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Checks or closed switch to ground in Park position. Different makes of "SCAN" testers wild read Park/Neutral signal differently. Refer to testers instruction manual for type of display used for specific tester.
Checks for an open switch in Drive or Reverse.
Be sure "SCAN" tester indicates Drive, even while wiggling shifter, to test for an intermittent or misadjusted switch in Drive.