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Diagnostic Procedures

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  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Check the Park/Neutral Position Switch and shift linkage for proper adjustment. If the Park/Neutral Position switch and shift linkage are properly adjusted, go to next step.
  3. Install the scan tool. Turn the ignition ON with the engine OFF. Record the DTC Failure Records. Using the scan tool, monitor PRNDL A, B, C, P status while moving the shift selector through each selector position. See PARK/NEUTRAL POSITION SWITCH LOGIC  table. Does each switch toggle ON and OFF in the correct sequence and does the range displayed on the scan tool match the actual range for the selector position chosen? If yes, see DIAGNOSTIC AIDS . If no, go to next step.
  4. Turn the ignition OFF. Disconnect the C2 connector at the TCM. Install J 39700 Breakout Box and J 43799 Breakout Box Adapter. Turn the ignition ON. In sequence, connect connector C2 pin No. 20 to connector C2 pins No. 5, 6, 7, and 8. See Fig 1. Using the scan tool, monitor PRNDL A, B, C, P status. See CONNECTOR PIN IDENTIFICATION  table. Does each switch toggle ON and OFF in the correct sequence as each pin is grounded? If yes, go to next step. If no, go to step  8.
    CONNECTOR PIN IDENTIFICATION

    Circuit Pin Number
    A 5
    B 6
    C 7
    P 8
  5. Turn the ignition OFF. Reconnect the C2 connector to the TCM. Disconnect the 4-pin connector at the Park/Neutral Position switch. Turn the ignition ON. Using the scan tool, monitor PRNDL A, B, C, P status. In sequence, connect pins 4A, 4B, 4C, and 4D in the 4-way PNP connector to pin 7D (use pin "H" on the J 44722 magnetic overlay for this operation) in the 7-way PNP connector (use J 39700 breakout box and J 44722 transmission harness to do this step). Does the scan tool indicate the status as ON? If yes, go to next step. If no, go to step  7.
  6. Replace the Park/Neutral Position Switch. After repairs, go to step  9.
  7. Inspect and repair the transmission wiring harness assembly. After repairs, go to step  9.
    8. NOTE: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM.
  8. Replace the TCM. After repairs, go to next step.
  9. To verify your repair, clear the DTC. Using the scan tool monitor PRNDL A, B, C, P status while moving the shift selector through each selector position. See PARK/NEUTRAL POSITION SWITCH LOGIC  table. Does each switch toggle ON and OFF in the correct sequence as the selector is moved? If yes, system is okay. If no, go to step  1.
PARK/NEUTRAL POSITION SWITCH LOGIC

Range (1) A (1) B (1) C (1) P
P Off On On Off
R Off Off On On
N On Off On Off
1 On On Off Off
2 Off On Off On
3 Off Off Off Off
4 - - - -
5 On Off Off On
(1) On - Open Circuit; Off - Grounded Circuit
Fig 1: Transmission Range Switch Wiring Diagram
G00058875Courtesy of GENERAL MOTORS CORP.
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