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Home >> Cadillac >> 2012 >> Escalade EXT >> Repair and Diagnosis >> External Pages >> Different car >> Section 990 (Data Communication System) >> Diagnostic Information and 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 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Test for less than 1 ohm between the DLC ground circuit terminal 5 and ground.
    • If greater than 1 ohm, test the ground circuit for open/high resistance.
  2. Ignition OFF, disconnect the harness connector of the BCM.
  3. Ignition ON, test for B+ between each voltage input circuit of the BCM and ground.
    • If less than specified, test each voltage output circuit of the BCM for a short to ground, and each voltage input circuit of the BCM for a short to ground or and open/high resistance. If the circuits test normal, replace the faulty module.
  4. Test for less than 1 ohm between each ground circuit of the BCM and ground.
    • If greater than the specified range, repair the ground circuit for an open/high resistance.
  5. Attempt to communicate with the electronic brake control module (EBCM). Communication should not be available.
    • If communication is established, test or replace the resistor.
  6. Ignition OFF, disconnect the harness connector of the suspension control module.
  7. Attempt to communicate with the EBCM. Communication should not be available.
    • If communication is established, test the serial data circuits for a short between them, short to ground or a short to voltage between the suspension control module and the terminator resistor. If the circuits test normal, replace the suspension control module.
  8. Ignition OFF, disconnect the harness connector of the distance sensing cruise control module.
  9. Attempt to communicate with the EBCM. Communication should not be available.
    • If communication is established, replace the cruise control module.
  10. Ignition OFF, disconnect the harness connector of the vehicle communication interface module (VCIM).
  11. Attempt to communicate with the EBCM. Communication should not be available.
    • If communication is established, test the serial data circuits for a short between them, short to ground or a short to voltage between the between the VCIM and the suspension control module. If the circuits test normal, replace the VCIM.
  12. Ignition OFF, disconnect harness connector C3 of the BCM.
  13. Test for infinite resistance between the serial data circuits of BCM harness connector C3 terminal 8 and ground and between BCM harness connector C3 terminal 9 and ground.
    • If less than the specified range, test the circuit for a short to ground.
  14. Ignition OFF, disconnect the harness connector of the ECM. Connect harness connector C3 of the BCM.
  15. Attempt to communicate with the EBCM. Communication should not be available.
    • If communication is established, replace the ECM.
  16. Ignition OFF, disconnect the harness connector of the transmission control module (TCM).
  17. Attempt to communicate with the EBCM. Communication should not be available.
    • If communication is established, test the serial data circuits for a short between them, short to ground or a short to voltage between the TCM and the ECM. If the circuits test normal, replace the TCM.
  18. Ignition OFF, connect the harness connector of the suspension control module. Disconnect the harness connector of the EBCM.
  19. Attempt to communicate with the suspension control module. Communication should not be available.
    • If communication is established, test the serial data circuits for a short between them, short to ground or a short to voltage between the EBCM and the TCM. If the circuits test normal, replace the EBCM.
  20. Ignition OFF, disconnect harness connector C3 of the BCM.
  21. Test for less than 1 volt between the high speed GMLAN serial data circuits of the DLC and ground.
    • If greater than the specified range, test the serial data circuit for a short to voltage.
  22. Test for infinite resistance between the high speed GMLAN serial data circuit of the DLC and ground.
    • If less than the specified range, test the serial data circuit for a short to ground.
  23. Test for infinite resistance between the high speed GMLAN serial data (+) and (-) circuits of the DLC.
    • If less than the specified range, test the serial data circuits for a short between them.
  24. If the circuits test normal, replace the BCM.
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