Code 31, Park/Neutral Switch Circuit
The park/neutral switch contacts are part of the neutral start switch. The 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 3-4 consecutive starts or if conditions occur as follows:
- No Code 29 exists.
- Circuit No. 434 indicates ground.
- Transmission is in high gear.
- TCC is locked on 4T60 trans. only.
- Vehicle speed is greater than 45 MPH and TPS is less than 15 percent (.94 volt) on 3T40 trans. only.
- All above conditions have been met for at least 12 seconds.NOTE: Test numbers refer to test numbers on diagnostic chart.
- This tests for a closed switch to ground in Park.
- This tests for an open switch in Drive.
- Be sure "Scan" tester indicates Drive, even when wiggling shifter.