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Verifying the Serial Data Circuits using Data Bus Diagnostic Tool

  1. Using schematics and vehicle build information, identify all low speed GMLAN devices the tested vehicle is equipped with and each device location on the low speed GMLAN serial data bus.
  2. Ignition ON.
  3. From Data Circuit input selection, select Terminal 1 to test the low speed GMLAN serial data bus.
  4. Start the test and verify that all applicable low speed GMLAN devices are displayed under the Control Module column of the Detected State tab.
    • If all low speed GMLAN devices are not responding 

      Refer to step 3 of Circuit/System Verification - Verifying the Serial Data Circuits using Digital Multimeter to test for a short to voltage or short to ground on the low speed GMLAN serial data circuit or an open/high resistance between the X84 Data Link Connector and the first low speed GMLAN device or splice pack.

    • If one or more low speed GMLAN devices are not responding 

      Refer to Circuit/System Testing - Testing the Device Circuits to test the non-communicating low speed GMLAN device closest to the X84 Data Link Connector.

    • If all low speed GMLAN devices are responding 
  5. All OK.
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