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Home >> Cadillac >> 2021 >> CT4 Sport, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 162 (Data Communications - Diagnostic Information And Procedures (2 Of 3)) >> Diagnostic Information and Procedures >> DTC U1345-U1349 >> 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:
  • A DTC in U1345 - U1349 range is normally used to indicate a LIN bus off. If a DTC in U1345 - U1349 range is set by itself, use the LIN schematics for the K20 Engine Control Module to identify the LIN slave device to diagnose it.
  • Use the schematics to identify the affected LIN serial data circuit mentioned in the DTC descriptor and all LIN devices on that circuit.
  • Use the connector end views to identify 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 K20 Engine Control Module. Do not disconnect the K20 Engine Control Module 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 K20 Engine Control Module.
    2. Test for infinite resistance between the serial data circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    3. Test for less than 2 Ω in the 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 K20 Engine Control Module.
    • If greater than 12 V 
    1. Ignition/Vehicle OFF, disconnect the harness connector at the K20 Engine Control Module.
    2. Ignition ON/Vehicle In Service Mode.
    3. Test for less than 1 V between the serial data circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    4. Replace the K20 Engine Control Module.
    • Go to next step: If between 3.5 - 12 V 
  4. Ignition/Vehicle OFF, disconnect the K20 Engine Control Module.
  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 K20 Engine Control Module 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 K20 Engine Control Module 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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