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Home >> Cadillac >> 2021 >> CT4 Sport, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 135 (12 V Starting And Charging - Diagnostic Information And Procedures) >> Diagnostic Information and Procedures >> DTC U3003 >> 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.
  1. Ignition "OFF" and all vehicle systems OFF, disconnect the harness connectors at the appropriate control module that is setting the DTC. It may take up to 2 min for all vehicle systems to power down.
  2. Test for less than 10 Ω between each ground circuit terminal and ground.
    • If 10 Ω or greater 
    1. ignition "OFF".
    2. Test for less than 2 Ω in the ground circuit end to end.
      • If the measured resistance is 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, repair the open/high resistance in the ground connection.
    • Go to next step: If less than 10 Ω 
  3. Verify a test lamp illuminates between each B+ circuit terminal and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. ignition "OFF".
    2. Test for less than 2 Ω in the B+ circuit end to end.
      • If the measured resistance is 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, 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. ignition "OFF".
    2. Test for infinite resistance between the B+ circuit and ground.
      • If the measured resistance is not infinite, repair the short to ground in the circuit.
      • If the measured resistance is infinity, replace the corresponding control module.
    • Go to next step: If the test lamp is ON 
    4. NOTE:

    If the component is not equipped with an ignition circuit proceed to Step 6.

  4. Ignition "ON".
  5. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Ignition "OFF".
    2. Test for less than 2 Ω in the ignition circuit end to end.
      • If the measured resistance is 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, 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. Ignition "OFF".
    2. Test for infinite resistance between the ignition circuit and ground.
      • If the measured resistance is not infinite, repair the short to ground in the circuit.
      • If the measured resistance is infinity, replace the corresponding control module.
    • Go to next step: If the test lamp is ON 
  6. Replace the appropriate control module.
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