DTC 31

Code 31 Chart:

Code 31 Wiring Diagram:

CIRCUIT DESCRIPTION:

The Park/Neutral switch input is grounded by the electronic PRNDL decoder in park or neutral and open in drive ranges.

The ECM supplies ignition voltage through a current limiting resistor to CKT 434 and senses a grounded input when the voltage on CKT 434 drops to less than one volt.

The ECM uses the P/N signal as one of the inputs to control, idle Speed (IAC), spark advance, and Vehicle Speed Sensor Diagnostics (VSS).

Code 31 will set if:

^ CKT 434 indicates an open for 3 consecutive starts.

^ CKT 434 indicates a ground.

^ No Code 38.

^ Transmission in high gear.

^ VSS greater than 45 mph and TPS less than 15% (0.94 volts).

^ Above conditions met for 12 seconds.

^ Code 31 does not illuminate the the "Service Engine Soon Light".


TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. Checks for a grounded P/N input in park position.

2. Checks for a faulty ECM.

3. Checks for an ungrounded P/N input in drive range. Be sure the scan tool display indicates drive even while wiggling the shifter. If it doesn't check for a misadjusted neutral safety switch or an intermittent.