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Home >> Cadillac >> 2016 >> CTS Base, RWD >> Repair and Diagnosis >> Engine Performance >> System >> Data Communication System >> Diagnostic Information and Procedures >> DTC U0074: Control Module Communication Powertrain Expansion CAN Bus Off Malfunction >> Circuit/System Testing >> Notes
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Circuit/System Testing: Notes

NOTE:

Each device may need to be disconnected to isolate a circuit fault.

Use the schematic to identify the following:

  • Powertrain high speed CAN devices the vehicle is equipped with
  • Powertrain high speed CAN serial data circuit terminating resistors
  • Device locations on the powertrain high speed CAN serial data circuits
  • Each device's ground, B+, ignition and powertrain high speed CAN serial data circuit terminals

Some devices with an internal terminating resistor have a loop in the harness that connects the internal terminating resistor to the serial data circuit. When wired this way, test these loop circuits for the appropriate failure mode short to voltage, short to ground or open/high resistance prior to replacing the device for each of the following tests.

  1. Ignition OFF, all access doors closed, all vehicle systems OFF and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors with the powertrain high speed CAN serial data circuits at an easily accessible device that is not communicating. It may take up to 2 minutes for all vehicle systems to power down. Refer to Data Link References  to determine which devices are on the powertrain expansion bus.
  2. Ignition ON.
  3. Test for less than 4.5 V between each powertrain high speed CAN serial data circuit at the device that was just disconnected and ground.
    • If 4.5 V or greater 

      Refer to Testing the Serial Data Circuits for a Short to Voltage.

    • If less than 4.5 V 
  4. Ignition OFF, all access doors closed, all vehicle systems OFF and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
  5. Test for greater than 100 Ω between each powertrain high speed CAN serial data circuit at the device that was just disconnected and ground.
    • If 100 Ω or less 

      Refer to Testing the Serial Data Circuits for a Short to Ground.

    • If greater than 100 Ω 
  6. Test for 110-130 Ω between each pair of the powertrain high speed CAN serial data circuits at the device that was just disconnected:
    • If less than 110 Ω 

      Refer to Testing the Serial Data Circuits for a Short between the Circuits.

    • If greater than 130 Ω 

      Refer to Testing the Serial Data Circuits for an Open/High Resistance.

    • If between 110-130 Ω 
  7. Refer to Testing the Device Circuits.
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