Powertrain Controls - ECM/PCM

Code Chart 31:

Park/Neutral Circuit:

CIRCUIT DESCRIPTION:
The Park/Neutral position switch contacts are a part of the neutral start switch and are closed to ground 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 closed switch when the voltage on CKT 434 drops to less than one volt. The ECM uses the PNP signal as one of the inputs to control, idle Speed (IAC), spark advance, and Vehicle Speed Sensor Diagnostics (VSS).

DTC 31 will set if:

^ Signal on CKT 434 indicates an open PNP switch for 3 consecutive starts.
OR
^ Signal on CKT 434 grounded.
^ No DTC 38.
^ TCC is locked (4T60 only).
^ Transmission in high gear.
^ VSS greater than 45 mph and TP sensor less than 20% (3T40 only).
^ Above conditions met for for 12 seconds.
DTC 31 does not illuminate the MIL.

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

1. Checks for a closed switch to ground in park position.

2. Checks for an open switch in drive range.

3. Be sure "Scan" indicates drive, even while wiggling shifter, to test for an intermittent or mis-adjusted switch in drive or overdrive range.