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Home >> Cadillac >> 2021 >> CT4 Sport, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 191 (Data Communications - Diagnostic Information And Procedures (3 Of 3)) >> Diagnostic Information and Procedures >> Scan Tool Does Not Communicate with Device on CAN 4 >> Circuit/System Verification

Circuit/System Verification

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NOTE:

Review and understand how to use the Network Communication Status function in scan tool prior to using the Network Communication Status section in this diagnostic procedure. Refer to Network Communication Status .

Perform Circuit/System Verification using one of the following two methods:

Verifying the communication status using Network Communication Status function

  1. Ignition ON/Vehicle In Service Mode.
  2. Verify that the scan tool is communicating with vehicle.
    • Go to next step: If the scan tool is communicating with vehicle 
  3. Ignition/Vehicle OFF, access the Network Communication Status application in scan tool under Vehicle Diagnostics > Vehicle Communication Diagnostics > Network Communication Status.
  4. Verify one or more CAN devices are not communicating. Refer to Network Communication Status  to determine the CAN devices that are not communicating.
    • If only one device is not communicating 

      Refer to Circuit/System Testing - Testing the Device Circuits  . The possible fault can be device's ground, power, or an open in the CAN serial data circuit between that non communicating device and the K56 Serial Data Gateway Module.

    • If two or more devices are not communicating, but not all 

      Refer to Circuit/System Testing - Testing the Device Circuits  . The possible fault can be an open in the CAN serial data circuit at the non communicating device closet to the K56 Serial Data Gateway Module. Use the schematic for CAN bus being tested to determine the non communicating device closest to the K56 Serial Data Gateway Module.

    • If all devices are not communicating 

      Refer to Circuit/System Testing - Serial Data Starting Point  . One of the following faults can occur:

    • A short to voltage in a CAN serial data circuit.
    • A short to ground in a CAN serial data circuit.
    • A short together between CAN serial data circuits.
    • An open/high resistance in a CAN serial data circuit between the K56 Serial Data Gateway Module and the closet non communicating device if the K56 Serial Data Gateway Module is at one end of the bus. Use the schematic for CAN bus being tested to determine the non communicating device closest to the K56 Serial Data Gateway Module.
    • Go to next step: If all CAN devices are communicating 
  5. A fault is currently not present and may be an intermittent condition.

Verifying the communication status using Digital Multimeter

  1. Ignition ON/Vehicle In Service Mode.
  2. Verify that the scan tool is communicating with vehicle.
    • Go to next step: If the scan tool is communicating with vehicle 
  3. Attempt to communicate with all devices on the CAN 4 bus. Refer to Data Link References , and Data Communication Wiring Schematics to determine how many devices should be communicating on the CAN 4 bus.
  4. Verify two or more devices are not communicating on the CAN 4 bus.
    • If only one device is not communicating 

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

    • Go to next step: If two or more devices are not communicating 
  5. Refer to Circuit/System Testing - Serial Data Starting Point  .
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