Code 31 - Park/Neutral Switch Circuit

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 3-4 consecutive starts or if conditions occur as follows:

• Code 38 does not exist.
• Circuit No. 434 indicates ground.
• Transmission is in high gear.
• TCC is locked (4T60 transaxle).
• TPS is less than 15 percent (.94 volt) and vehicle speed is greater than 45 MPH (3T40 transaxle).
• All above conditions have been met for at least 12 seconds.
  NOTE: Test numbers refer to numbers on diagnostic chart.

1. Checks for a grounded PNP input in park position.
2. Checks for a faulty ECM
3. Checks for an ungrounded PNP input in drive range. Be sure Tech 1 display indicates drive, even while wiggling shifter. If it doesn't, check for a misadjusted transmission range switch or an intermittent.
   Fig 1: Code 31 Schematic ("A" Body) Park/Neutral Switch Circuit

   
   Fig 2: Code 31 Schematic ("N" Body) Park/Neutral Switch Circuit

   
   Fig 3: Code 31