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Home >> Cadillac >> 2012 >> Escalade EXT >> Repair and Diagnosis >> External Pages >> Different car >> Section 1133 (Data Communication System) >> Diagnostic Information and Procedures >> Scan Tool Does Not Communicate with High Speed GMLAN Device >> Circuit/System Testing >> Diagnostic 1
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Diagnostic 1

WARNING: This page is about a different car, the 2008 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
  1. Connect the harness connector at the TCC module.
  2. Remove the terminator resistor.
  3. Test for 108-132 ohms of resistance between terminals A and B of the terminator resistor.
    • If not within the specified range, replace the resistor.
  4. Connect the harness connector at the terminator resistor.
  5. Ignition OFF, disconnect the X3 harness connector at the BCM.
  6. Ignition OFF, test for less than 2 ohms of resistance between the DLC serial data circuit terminal 6 and BCM serial data circuit terminal 16.
    • If greater than the specified range, test the serial data circuit for open/high resistance.
  7. Ignition OFF, disconnect the X4 harness connectors at the BCM.
  8. Test for less than 5 ohms of resistance between the following ground circuit terminals and ground.
    • X3 terminal 1
    • X3 terminal 5
    • X4 terminal 9
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  9. Ignition ON, verify a test lamp illuminates between the following B+ circuit terminals and ground.
    • X2 terminal 2
    • X3 terminal 2
    • X3 terminal 3
    • X4 terminal 1
    • X4 terminal 2
    • X4 terminal 3
    • X4 terminal 4
    • X4 terminal 10
    • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the B+ output circuits for a short to ground.
  10. Ignition OFF, test for infinite resistance between the following serial data circuits of the DLC and ground.
    • Terminal 6
    • Terminal 14
    • If less than the specified value, test the serial data circuits for a short to ground.
  11. Ignition ON, test for less than 1-volt between the following serial data circuits of the DLC and ground.
    • Terminal 6
    • Terminal 14
    • If greater than the specified range, test the serial data circuit for a short to voltage.
  12. Ignition OFF, test for infinite resistance between the DLC serial data circuit terminal 6 and terminal 14.
    • If less than the specified value, test for a short between the serial data circuits.
  13. Connect the X3 and X4 harness connector at the BCM.
  14. Ignition OFF, disconnect the harness connector at the VCIM.
  15. Ignition ON, attempt to communicate with the TCC module. Communication should not be available.
    • Replace the VCIM.
  16. Ignition OFF, disconnect the harness connector at the noise filter.
  17. Ignition ON, attempt to communicate with the TCC module. Communication should not be available.
    • If communication is established, test the following serial data circuits between the noise filter and the VCIM, and the noise filter and the terminator resistor for a short between the circuits, short to ground or a short to voltage. If the circuits test normal, replace the noise filter.
      • Noise filer terminal 3 VCIM terminal 28
      • Noise filter terminal 4 VCIM terminal 14
      • Noise filter terminal 3 and terminal 4
      • Noise filter terminal 3 terminator resistor terminal A
      • Noise filter terminal 4 terminator resistor terminal B
  18. Ignition OFF, disconnect the X3 harness connector at the BCM.
  19. Ignition OFF, test for infinite resistance between the following serial data circuits and ground.
    • Terminal 16
    • Terminal 17
    • If less than the specified value, test the serial data circuit for a short to ground.
  20. Ignition ON, test for less than 1-volt between the following serial data circuits and ground.
    • Terminal 16
    • Terminal 17
    • If greater than the specified range, test the serial data circuit for a short to voltage.
  21. Ignition OFF, test for infinite resistance between the serial data circuit terminal 16 and terminal 17.
    • If less than the specified value, test for a short between the serial data circuits.
  22. If the circuits test normal, replace the BCM.
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