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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:
  • A DTC in U1500-U15FF range is normally used to indicate a LIN bus off. If a DTC in U1500-U15FF range is set by itself, use the LIN schematics for the device setting this DTC to identify the LIN slave device to diagnose it.
  • Use the schematic to identify the following:
    • The master control module and the LIN devices on the same LIN serial data circuit
    • The master control module's LIN serial data circuit terminal and the LIN device's B+, ignition, ground, and LIN serial data circuit terminals
  1. Ignition/Vehicle OFF, disconnect all LIN devices that share the same LIN serial data circuit with the control module setting the DTC. Do not disconnect the control module setting the DTC at this test step.
  2. Ignition ON/Vehicle In Service Mode.
    3. NOTE:

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

  3. 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 
  4. Ignition/Vehicle OFF, disconnect the control module setting the DTC.
  5. Reconnect the first LIN device.
  6. Ignition ON/Vehicle In Service Mode.
  7. 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 
  8. Ignition/Vehicle OFF, reconnect another LIN device.
  9. Ignition ON/Vehicle In Service Mode.
  10. 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 
  11. Repeat steps 8-10 for the remaining LIN devices until a faulty LIN device is identified.
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