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Home >> Cadillac >> 2017 >> CT6 Plug-In >> Repair and Diagnosis >> Engine Performance >> System >> Data Communication System - DTC B1000 To DTC U1818 >> Diagnostic Information and Procedures >> DTC U007D: Control Module Communication Low Speed Extension CAN Bus Off >> Circuit/System Verification
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Circuit/System Verification

  1. Ignition ON/Vehicle In Service Mode.
  2. Verify that DTC U0073, U0074, U0075, U0077, U0078, U007A, P06E4, P1EB9, U1814, U2099, B1325, B1330, B1370, B1380, B1424, B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560 or P0562 is not set.
    • If none of the DTCs are set 
  3. Attempt to communicate with all devices on the gateway isolated low speed GMLAN serial data circuit. Refer to Data Link References to determine which devices are on the gateway isolated low speed GMLAN bus.
  4. Verify that all gateway isolated low speed GMLAN devices are communicating.
    • If only one device is not communicating 

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

    • If all devices are not communicating, except the K56 Serial Data Gateway Module 

      Refer to Circuit/System Testing.

    • If two or more devices are not communicating but not all, except the K56 Serial Data Gateway Module 

      Refer to Circuit/System Testing - Testing the Serial Data Circuits for an Open/High Resistance.

    • If all devices are communicating 
  5. All OK.
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