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Home >> Cadillac >> 2016 >> CTS V >> Repair and Diagnosis >> Engine Performance >> System >> Data Communication System >> Diagnostic Information and Procedures >> Scan Tool Does Not Communicate with High Speed GMLAN Device >> Circuit/System Verification >> Verifying the Serial Data Circuits using Data Bus Diagnostic Tool
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Verifying the Serial Data Circuits using Data Bus Diagnostic Tool

  1. Using schematics and vehicle build information, identify all high speed GMLAN devices the tested vehicle is equipped with, terminating resistors and each device location on the high speed GMLAN bus.
  2. Ignition ON/Vehicle In Service Mode.
  3. From Data Circuit input selection, select Terminal 6, 14 to test the high speed GMLAN serial data bus.
  4. Start the test and verify the Detected State parameter is displayed as OK.
    • If the Detected State parameter is displayed as Control Module Not Awake 

      Refer to Circuit/System Testing - Testing the Device Circuits.

    • If the Detected State parameter is displayed as Control Module Ground Connection Malfunction 

      Refer to Circuit/System Testing - Testing the Device Circuits.

    • If the Detected State parameter is displayed as CAN Bus [+] (pin 6) Circuit Shorted to High Voltage or CAN Bus [-] (pin 14) Circuit Shorted to High Voltage 

      Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Voltage.

    • If the Detected State parameter is displayed as CAN Bus [+] (pin 6) Circuit Shorted to Low Voltage or CAN Bus [-] (pin 14) Circuit Shorted to Low Voltage 

      Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Ground.

    • If the Detected State parameter is displayed as CAN Bus [-] Shorted to Bus [+] 

      Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short between the Circuits.

    • If the Detected State parameter is displayed as CAN Bus Open with one or more non responding high speed GMLAN devices 

      Refer to Circuit/System Testing - Testing the Serial Data Circuits for an Open/High Resistance (Data Bus Diagnostic Tool).

    • If the Detected State parameter is displayed as CAN Bus Open and all high speed GMLAN devices are responding 

      Repair the open/high resistance in the circuit between the external terminating resistor and the closet responding device.

    • If the Detected State parameter is displayed as OK and none of the high speed GMLAN devices are responding 

      Repair the open/high resistance in the circuit between the X84 Data Link Connector and the first splice/device in the serial data circuit. If the circuit tests normal, check the MDI cable and the connection at X84 Data Link Connector prior to replacing the first device or splice pack.

    • If the Detected State parameter is displayed as OK and one or more high speed GMLAN devices are not responding 

      Refer to Circuit/System Testing - Testing the Device Circuits to test the non responding device closest to a responding device.

    • If the Detected State parameter is displayed as OK and all high speed GMLAN devices are responding 
  5. All OK.
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