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Home >> Cadillac >> 2021 >> CT4 Sport, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 191 (Data Communications - Diagnostic Information And Procedures (3 Of 3)) >> Diagnostic Information and Procedures >> DTC U241C >> 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.

  1. Ignition ON/Vehicle In Service Mode.
  2. Verify the K20 Engine Control Module is not communicating.
    • If the device is still communicating 
    1. Ignition/Vehicle OFF, disconnect all the harness connectors at the K20 Engine Control Module.
    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 K20 Engine Control Module.
  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 K20 Engine Control Module.
    • 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 K20 Engine Control Module.
    • Go to next step: If the test lamp illuminates 
  8. Test for less than 4.5 V between each of the CAN 2 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 2 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 2 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. Disconnect the harness connectors at the K56 Serial Data Gateway Module.
  13. Test for less than 2 Ω in each of the CAN 2 serial data circuits end to end between the K20 Engine Control Module and the K56 Serial Data Gateway Module.
    • If 2 Ω or greater 

      Repair the open/high resistance in the CAN 2 serial data circuit between the K20 Engine Control Module and the K56 Serial Data Gateway Module.

    • Go to next step: If less than 2 Ω 
  14. Inspect both harness and component connectors for contamination, corrosion, and terminal tension.
  15. Reconnect the harness connectors at the K20 Engine Control Module and the K56 Serial Data Gateway Module.
  16. Ignition ON/Vehicle In Service Mode.
  17. Verify the DTC is not set again.
    • If the DTC is set 

      Replace the K20 Engine Control Module.

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