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Home >> Cadillac >> 2021 >> CT4 Sport, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 162 (Data Communications - Diagnostic Information And Procedures (2 Of 3)) >> Diagnostic Information and Procedures >> DTC U1100-U12FF >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2022 Cadillac CT4. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:

Use the schematics and connector end views to identify the device's ground, B+, ignition, and serial data circuit terminals.

Testing a CAN Device

  1. Ignition ON/Vehicle In Service Mode.
  2. Verify the device is not communicating.
    • If the device is still communicating 
    1. Ignition/Vehicle OFF, disconnect all the harness connectors at the CAN device specified by the DTC descriptor.
    2. Ignition ON/Vehicle In Service Mode, refer to step 8 to diagnose a fault in the serial data circuits.
    • Go to next step: If the device is not communicating 
  3. Ignition/Vehicle OFF, disconnect all the harness connectors at the CAN device that is not communicating.
  4. Verify a test lamp illuminates between each of the ground circuit terminals and B+.
    • If the test lamp does not illuminate 

      Repair the open/high resistance in the ground circuit or ground connection.

    • Go to next step: If the test lamp illuminates 
  5. Ignition ON/Vehicle In Service Mode.
  6. If equipped, verify a test lamp illuminates between each of the B+ circuit terminals and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Test for an open/high resistance in the B+ circuit.
      • If an open/high resistance is found, repair the fault in the circuit.
      • Go to next step: If an open/high resistance is not found
    2. Verify the fuse is not open and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Test for a short to ground in the B+ circuit.
      • If a short to ground is found, repair the fault in the circuit.
      • Go to next step: If a short to ground is not found
    2. Replace the disconnected device.
    • Go to next step: If the test lamp illuminates 
  7. If equipped, verify a test lamp illuminates between each of the ignition circuit terminals, which has a fuse in the circuit, and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Test for an open/high resistance in the ignition circuit.
      • If an open/high resistance is found, repair the fault in the circuit.
      • Go to next step: If an open/high resistance is not found
    2. Verify the fuse is not open and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Test for a short to ground in the ignition circuit.
      • If a short to ground is found, repair the fault in the circuit.
      • Go to next step: If a short to ground is not found
    2. Replace the disconnected device.
    • Go to next step: If the test lamp illuminates 
  8. Test for less than 4.5 V between each of the CAN Bus serial data circuit terminals and ground.
    • Go to next step: If less than 4.5 V 
  9. Ignition/Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 10 min for all vehicle systems to power down.
  10. Test for greater than 100 Ω between each of the CAN Bus serial data circuit terminals and ground.
    • Go to next step: If greater than 100 Ω 
  11. Test for less than infinite resistance between each of the CAN Bus serial data circuit terminals and ground.
    • If infinite resistance 

      Repair the open/high resistance in the serial data circuit.

    • Go to next step: If less than infinite resistance 
    12. NOTE:

    The following test step is only applicable to a CAN device with 2 pairs of serial data circuits or a CAN device with an internal terminating resistor.

  12. Test for 110-130 Ω between each pair of the CAN Bus serial data circuits.
    • If less than 110 Ω 

      Refer to an appropriate diagnostic procedure below to test for a short between the serial data circuits.

    • If greater than 130 Ω 

      Refer to an appropriate diagnostic procedure below to test for an open/high resistance in the serial data circuit.

    • Go to next step: If between 110-130 Ω 
  13. Inspect both harness and component connectors for contamination, corrosion, and terminal tension.
  14. Reconnect the harness connectors at the CAN device.
  15. Ignition ON/Vehicle In Service Mode.
  16. Verify the DTC is not set again.
    • If the DTC is set 

      Replace the device that is not communicating.

    • Go to next step: If the DTC is not set 
  17. A fault is currently not present and may be an intermittent condition.

Testing a LIN Device

  1. Ignition/Vehicle OFF, disconnect all the harness connectors at the LIN device that is not communicating.
  2. Verify a test lamp illuminates between each of the ground circuit terminals and B+.
    • If the test lamp does not illuminate 

      Repair the open/high resistance in the ground circuit or ground connection.

    • Go to next step: If the test lamp illuminates 
  3. Ignition ON/Vehicle In Service Mode.
  4. If equipped, verify a test lamp illuminates between each of the B+ circuit terminals and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Test for an open/high resistance in the B+ circuit.
      • If an open/high resistance is found, repair the fault in the circuit.
      • Go to next step: If an open/high resistance is not found
    2. Verify the fuse is not open and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Test for a short to ground in the B+ circuit.
      • If a short to ground is found, repair the fault in the circuit.
      • Go to next step: If a short to ground is not found
    2. Replace the disconnected device.
    • Go to next step: If the test lamp illuminates 
  5. If equipped, verify a test lamp illuminates between each of the ignition circuit terminals, which has a fuse in the circuit, and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Test for an open/high resistance in the ignition circuit.
      • If an open/high resistance is found, repair the fault in the circuit.
      • Go to next step: If an open/high resistance is not found
    2. Verify the fuse is not open and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Test for a short to ground in the ignition circuit.
      • If a short to ground is found, repair the fault in the circuit.
      • Go to next step: If a short to ground is not found
    2. Replace the disconnected device.
    • Go to next step: If the test lamp illuminates 
  6. If equipped, verify a test lamp illuminates between each of the ignition circuit terminals, which is controlled by a control module, and ground.
    • If the test lamp does not illuminate 
    1. Ignition/Vehicle OFF, remove the test lamp, disconnect the harness connectors at the control module that controls the ignition circuit and all devices that share the same ignition circuit.
    2. Test for infinite resistance between the ignition circuit and ground.
      • If less than infinite resistance, repair the short to ground in the circuit.
      • Go to next step: If infinite resistance
    3. Test for less than 2 Ω in the ignition circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • Go to next step: If less than 2 Ω
    4. Reconnect the control module that controls the ignition circuit.
    5. Ignition ON/Vehicle In Service Mode.
    6. Verify a test lamp illuminates between the ignition circuit terminal and ground.
      • If the test lamp does not illuminate, replace the control module that controls the ignition circuit.
      • Go to next step: If the test lamp illuminates
    7. Ignition/Vehicle OFF, reconnect the first device that shares the same ignition circuit.
    8. Ignition ON/Vehicle In Service Mode.
    9. Verify a test lamp illuminates between the ignition circuit terminal and ground.
      • If the test lamp does not illuminate, replace the device that was just connected.
      • If the test lamp illuminates and there are more devices to connect, connect the next device and repeat step 6.9 until there are no more devices to connect.
    • Go to next step: If the test lamp illuminates 
  7. Ignition/Vehicle OFF, disconnect all LIN devices that share the same LIN serial data circuit.
  8. Ignition ON/Vehicle In Service Mode.
    9. NOTE:

    For accurate voltage reading, disconnect the battery charger prior to performing the following test step.

  9. Test for 3.5-12 V between the LIN serial data circuit terminal and ground.
    • If less than 3.5 V 
    1. Ignition/Vehicle OFF, disconnect the harness connector at the control module setting the DTC.
    2. Test for infinite resistance between the LIN serial data circuit terminal and ground.
      • If less than infinite resistance, repair the short to ground in the circuit.
      • Go to next step: If infinite resistance
    3. Test for less than 2 Ω in the LIN serial data circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • Go to next step: If less than 2 Ω
    4. Replace the control module that sets the DTC.
    • If greater than 12 V 
    1. Ignition/Vehicle OFF, disconnect the harness connector at the control module setting the DTC.
    2. Ignition ON/Vehicle In Service Mode.
    3. Test for less than 1 V between the LIN serial data circuit terminal and ground.
      • If 1 V or greater, repair the short to voltage in the circuit.
      • Go to next step: If less than 1 V
    4. Replace the control module that sets the DTC.
    • Go to next step: If between 3.5-12 V 
  10. Verify how many LIN devices are connected to this LIN circuit.
    • If there is only one LIN device 
    1. Ignition/Vehicle OFF, inspect both harness and component connectors for contamination, corrosion, and terminal tension.
    2. Reconnect the harness connectors at the LIN device. Verify all connectors/terminals are fully seated.
    3. Ignition ON/Vehicle In Service Mode.
    4. Verify the DTC is not set again.
      • If the DTC is set, replace the LIN device that is not communicating.
      • Go to next step: If the DTC is not set
    5. A fault is currently not present and may be an intermittent condition.
    • Go to next step: If there are two or more LIN devices 
  11. Ignition/Vehicle OFF, disconnect harness connectors at the control module setting the DTC.
  12. Reconnect the harness connectors at the first LIN device.
  13. Ignition ON/Vehicle In Service Mode.
  14. Test for 3.5-12 V between the LIN serial data circuit terminal at the control module setting the DTC and ground.
    • If less than 3.5 V or greater than 12 V 

      Replace the LIN device that was just connected.

    • Go to next step: If between 3.5-12 V 
  15. Ignition/Vehicle OFF, reconnect the harness connectors at another LIN device.
  16. Ignition ON/Vehicle In Service Mode.
  17. Test for 3.5-12 V between the LIN serial data circuit terminal at the control module setting the DTC and ground.
    • If less than 3.5 V or greater than 12 V 

      Replace the LIN device that was just connected.

    • Go to next step: If between 3.5-12 V 
  18. Repeat steps 15-17 for the remaining LIN devices until a faulty LIN device is identified. If there is no faulty LIN device, replace the LIN device that is not communicating.
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