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Home >> Isuzu >> 2007 >> Ascender RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 307 (Data Communication System) >> Diagnostic Information & Procedures >> Scan Tool Does Not Communicate with High Speed GMLAN Device >> Circuit/System Testing
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Circuit/System Testing

WARNING: This page is about a different car, the 2008 Isuzu Ascender, 2008 GMC Envoy, and 2008 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the harness connector of the transmission control module (TCM).
  2. Test for 108-132 ohms between the serial data circuit terminal 6 and terminal 7.
    • If less than the specified range, test the serial data circuits for a short between them. If the circuits test normal, replace the 120 ohm resistor.
    • If greater than the specified range, test the serial data circuits for open/high resistance. If the circuits test normal, replace the 120 ohm resistor.
  3. Ignition ON, test for less than 1.0 volt between the serial data circuit terminal 6 and ground, and between terminal 7 and ground.
    • If greater than the specified range, test the serial data circuit for a short to voltage.
  4. Test for infinite resistance between the serial data circuit terminal 6 and ground, and between terminal 7 and ground.
    • If less than the specified value, test the serial data circuit for a short to ground.
  5. Test for 108-132 ohms between the serial data circuit terminal 37 and terminal 38.
    • If less than the specified range, test the serial data circuits for a short between them. If the circuits test normal, replace the ECM.
    • If greater than the specified range, test the serial data circuits for open/high resistance. If the circuits test normal, replace the ECM.
  6. Ignition ON, test for less than 1.0 volt between the serial data circuit terminal 37 and ground, and between terminal 38 and ground.
    • If greater than the specified range, test the serial data circuit for a short to voltage. If the circuits test normal, replace the ECM.
  7. Test for infinite resistance between the serial data circuit terminal 37 and ground, and between terminal 38 and ground.
    • If less than the specified value, test the serial data circuit for a short to ground. If the circuits test normal, replace the ECM.
  8. If the circuits test normal, replace the TCM.
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