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Home >> Chevrolet >> 2015 >> Volt >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Data Communication System - DTC B1000 To DTC U183E >> Diagnostic Information and Procedures >> DTC U0074: Control Module Communication Powertrain Expansion >> Circuit/System Verification

Circuit/System Verification

  1. Vehicle in Service Mode.
  2. Verify two or more devices are not communicating on the powertrain high speed GMLAN serial data circuit. Refer to Data Link References to determine how many devices should be communicating on the bus.
    • If two or more devices are not communicating 
  3. Vehicle OFF, all access doors closed, all vehicle systems OFF and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the scan tool from the X84 data link connector. The following tests will be done at the X84B auxiliary data connector. It may take up to 2 minutes for all vehicle systems to power down.
  4. Test for less than 10 Ω between the ground circuit terminal 5 and ground.
    • If 10 Ω or greater 
    1. Vehicle OFF.
    2. Test for less than 2 Ω in the ground circuit end to end.
      • If 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.
    • If less than 10 Ω 
  5. Vehicle in Service Mode.
  6. Test for less than 4.5 V between the serial data circuits listed below and ground.
    • Terminal 12
    • Terminal 13
    • If less than 4.5 V 
  7. Vehicle 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.
  8. Test for greater than 100 Ω between the serial data circuits listed below and ground.
    • Terminal 12
    • Terminal 13
    • If greater than 100 Ω 
  9. Test for 50-70 Ω between the serial data circuit terminals 12 and 13.
    • If between 35-50 Ω 

      There may be a third terminating resistor between the serial data circuits. This can happen if the incorrect device is installed. Some devices are available with and without the terminating resistors installed to reduce the need of terminating resistors in the wiring harness. Refer to Testing the Serial Data Circuits for a Short between the Circuits  .

    • If infinite resistance 

      Repair the open/high resistance in the circuit between the X84B auxiliary data connector and the first splice/device in the serial data circuit.

    • If between 50-70 Ω 
  10. Refer to Testing the Device Circuits  .
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