Code 31, Park/Neutral Switch Circuit - 3.8L: Notes

NOTE: Complete diagnosis of Code 31 for 3.8L requires GM Tech 1 scan tester, which is capable of indicating status of all 4 park/neutral switch positions. This chart does not apply to 3.8L (VIN L) "C", "E" and "H" body vehicles. Schematics for these models are supplied for reference purposes only.

Park/neutral switch contacts are part of neutral start switch. Contacts close to ground in Park or Neutral and open in Drive. Code 31 will set if park/neutral signal circuit indicates an open for 3 consecutive starts or if conditions occur as follows with ignition on and engine off.

Vehicle speed is zero MPH.
Gear selector switch indicates a gear other than Park or Neutral.
Gear selector status indicates an incorrect combination of LO and HI for more than 10 seconds.

Code 31 does not turn on SERVICE ENGINE SOON light.

NOTE: Test numbers refer to numbers on diagnostic chart.

This tests for proper operation of gear selector switch.
This tests for proper operation of gear selector switch.
Tests for an open of grounded circuit.