Powertrain Controls - ECM/PCM

Code 31 Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION:

The Park/Neutral switch contacts are a part of the neutral start switch. They are open in drive and closed in Park or Neutral.

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 P/N signal as one of the inputs to control:

^ Idle Speed (IAC).
^ Exhaust Gas Recirculation (EGR).
^ Spark timing
^ Fuel Control

Code 31 symptoms:

^ CKT 434 indicates P/N (grounded) while in drive range, 4th gear TCC engaged, EGR would be inoperative, resulting in possible detonation.
^ CKT 434 indicates drive (open) at start up, a dip in the idle may exist when the gear selector is moved into drive range.
^ Transaxle 4th gear switch has an intermittent open, the ECM thinks vehicle is in 4th gear and will set a Code 31.

NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to ECM CONNECTOR IDENTIFICATION under ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS for correct color code identification of circuit.

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

1. Checks for a closed switch to ground in park position. Different makes of "Scan" tools will read P/N differently.

Code 31 will set if:

^ CKT 434 indicates an open for 4 consecutive starts.
^ CKT 434 indicates a grounded circuit when transmission in 4th gear, TCC engaged and no Code 29 for 10 seconds.

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.