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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 81 (Engine Controls - Self-Diagnostics - 8.1L) >> Diagnostic Tests >> DTC P1781: TCM Mil Request Circuit >> Diagnostic Procedures

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. Connect a scan tool. Did DTC P1781 fail this ignition cycle? If yes, go to step  4. If no, go to next step.
  3. Observe the Freeze Frame/Failure Records data for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC or as close to the Freeze Frame/Failure Records data that you observed. Does the DTC fail this ignition cycle? If yes, go to next step. If no, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  4. Turn OFF the ignition. Disconnect the TCM. Connect a Digital Multimeter (DMM) from the TCM MIL request circuit at the TCM harness connector to a good ground. Turn ON the ignition, with the engine OFF. Does the voltage measure near battery voltage? If yes, go to next step. If no, go to step  6.
  5. Test the TCM MIL request circuit for a short to voltage. Repair as necessary. Did you find and correct a condition? If yes, go to step  12. If no, go to step  7.
  6. Test the TCM MIL request circuit for an open. Repair as necessary. Did you find and correct a condition? If yes, go to step  12. If no, go to step  7.
  7. Leave the TCM disconnected. Connect a fused jumper wire from the TCM MIL request circuit in the TCM harness connector to a good ground. Clear the DTCs with a scan tool. Does DTC P0700 set, not setting P1781? If yes, go to next step. If no, go to step  10.
  8. Test the TCM connectors for a bad connection. Did you find and correct a condition? If yes, go to step  12. If no, go to next step.
  9. Replace the TCM. After repairs, go to step  12.
  10. Test the PCM connectors for a bad connection. Did you find and correct a condition? If yes, go to step  12. If no, go to next step.
  11. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  12. Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  13. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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