Code 31, Park/Neutral Switch Circuit - 3.3L PFI (VIN N)

Fig 1: Code 31, Park/Neutral Switch Circuit Diagram (Achieva)

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Fig 2: Code 31, Park/Neutral Switch Circuit Diagram (Skylark)

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Fig 3: Code 31, Park/Neutral Switch Circuit Diagram (Grand Am)

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ECM supplies ignition voltage through a current limiting resistor to circuit No. 434 and senses a closed switch when voltage on circuit No. 434 drops to less than one volt. ECM uses Park/Neutral signal as one of the inputs to control Idle Speed Control (IAC), spark timing and Vehicle Speed Sensor (VSS). Code 31 will set under the following conditions:

• Circuit No. 434 indicates ground.
• No Code 38.
• Transmission is in high gear
• VSS greater than 45 MPH and TPS is less than .94 volt.
• Above conditions are met for 12 seconds.

Code 31 does not illuminate "Service Engine Soon" light.

1. This test checks for a closed switch to ground in park position.
2. This test checks for a faulty ECM.
3. This test checks for an ungrounded Park/Neutral input in drive range. Ensure scan tool indicates drive, even while wiggling shifter. If scan tool does not indicate as previously described, check for a misadjusted neutral safety switch or and intermittent problem.

Fig 4: Code 31, Troubleshooting Diagram (3.3L PFI - VIN N)

Courtesy of GENERAL MOTORS CORP.