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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. This code indicates that the TCM did not see the proper input signal for service brake status during an acceleration or deceleration cycle. This may indicate an open or short in the TCC Brake Switch/Cruise Control Release Circuit or a faulty stop lamp switch. Is the problem cause known? If yes, repair as necessary. After repairs, go to step  10. If no, go to next step.
  3. Install the scan tool. Turn the ignition to the RUN position with the engine OFF. Record the DTC Failure Record Data. Apply and release the service brake. Does the scan tool indicate that the brake switch is toggling off and on? If yes, see DIAGNOSTIC AIDS . If no, go to next step.
  4. With J 39200 Digital Multimeter (DMM), probe pins No. 5 and 7 on the C1 connector. See Fig 1. Apply and release the service brake. There should be no voltage reading at pin No. 7 when the brake is applied, with the brake released there should be 12V. Was voltage reading proper? If yes, go to step  9. If no, go to next step.
  5. Go to the stop lamp switch. With J 39200 DMM, probe pin "C" at the switch. See Fig 1. Supply a ground connection at the other lead. Apply and release the service brake. Is the switch turning voltage ON and OFF? If yes, go to step  7. If no, go to next step.
  6. With J 39200 DMM, measure voltage at pin "D" on the input side of the stop lamp switch. Is voltage available? If yes, go to step  8. If no, repair power feed to stop lamp switch.
  7. Replace the TCC Brake Switch/Cruise Control wiring harness. After repairs, go to step  10.
  8. Repair or replace the stop lamp switch. After repairs, go to step  10.
    9. NOTE: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM.
  9. Replace the TCM. After repairs, go to next step.
  10. In order to verify your repair, clear the DTC and operate the vehicle under normal driving conditions. Did the DTC return? If yes, go to step  1. If no, system is okay.
Fig 1: Brake Switch Wiring Diagram (Allison A/T)
G00058874Courtesy of GENERAL MOTORS CORP.
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