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Home >> Chevrolet >> 2012 >> Impala Police, Gas >> Repair and Diagnosis >> External Pages >> Different car >> Section 862 (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 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.
  1. Test for less than 1.0 ohm of resistance between the DLC ground circuit terminal 5 and ground.
    • If greater than the specified range, test the ground circuit for open/high resistance.
  2. Remove the terminator resistor.
  3. Test for 110-130 ohms of resistance between the terminals of the resistor.
    • If not within the specified range, replace the resistor.
  4. Ignition OFF, disconnect the harness connector X 3 of the BCM.
  5. Ignition ON, test for less than 1 volt between the high speed GMLAN serial data circuit of the DLC terminal 6 and ground, and terminal 14 and ground.
    • If greater than the specified range, test the serial data circuit for a short to voltage.
  6. Test for infinite resistance between the high speed GMLAN serial data circuit of the DLC terminal 6 and ground, and terminal 14 and ground.
    • If less than the specified value, test the serial data circuit for a short to ground.
  7. Test for infinite resistance between the high speed GMLAN serial data circuits of the DLC terminal 6 and 14.
    • If less than the specified value, test the serial data circuits for a short between them.
  8. Test for less than 2 ohms of resistance in the GMLAN serial data circuit between the DLC terminal 6 and BCM terminal 16.
    • If greater than the specified range, test the GMLAN serial data circuit for open/high resistance.
  9. Ignition OFF, connect the terminator resistor, and disconnect the harness connector X 4 of the BCM.
  10. Verify a test lamp illuminates between each ground circuit terminal of the BCM listed below and B+.
    • X 3 terminal 1
    • X 3 terminal 5
    • X 4 terminal 9
    • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  11. Ignition ON, verify a test lamp illuminates between each B+ circuit terminal of the BCM listed below and ground.
    • X 4 terminal 1
    • X 4 terminal 3
    • X 4 terminal 4
    • If the test lamp does not illuminate, test the B+ circuit for an open/high resistance or short to ground.
  12. Connect the harness connectors of the BCM.
  13. Ignition OFF, disconnect the harness connector of the ECM as listed:
    • RPO LS4 - X3
    • RPO LZE, LZ4 or LZ8 - X1
  14. Attempt to communicate with the BCM. Communication should not be available.
    • If communication is established, replace the ECM.
  15. Ignition OFF, disconnect the harness connector of the TCM.
  16. Attempt to communicate with the BCM. Communication should not be available.
    • If communication is established, test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the TCM and the ECM. If the circuits test normal, replace the TCM.
  17. Ignition OFF, disconnect the harness connector of the EBCM, if equipped. Attempt to communicate with the BCM. Communication should not be available.
    • If communication is established, test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the EBCM and the TCM. If the circuits test normal, replace the EBCM.
  18. Ignition OFF, disconnect the harness connector X3 of the BCM.
  19. Ignition ON, test for less than 1 volt between the serial data circuits of BCM terminal 8 and ground, and between BCM terminal 9 and ground.
    • If greater than the specified range, test the circuit for a short to voltage.
  20. Test for infinite resistance between the serial data circuits of BCM terminal 8 and ground, and between BCM terminal 9 and ground.
    • If less than the specified value, test the circuit for a short to ground.
  21. Test for infinite resistance between the serial data circuits of BCM terminal 8 terminal 9.
    • If less than the specified value, test the serial data circuits for a short between them.
  22. If the circuits test normal, replace the BCM.
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