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Circuit/System Testing: Notes

WARNING: Always perform the High Voltage Disabling procedure prior to servicing any High Voltage component or connection. Personal Protection Equipment (PPE) and proper procedures must be followed.

The High Voltage Disabling procedure includes the following steps:

  • Identify how to disable high voltage.
  • Identify how to test for the presence of high voltage.
  • Identify condition under which high voltage is always present and personal protection equipment (PPE) and proper procedures must be followed.

Before working on any high voltage system, be sure to wear the following Personal Protection Equipment:

  • Safety glasses with appropriate side shields when within 15 meters (50 feet) of the vehicle, either indoors or outdoors.
  • Certified and up-to-date Class "0" Insulation gloves rated at 1000V with leather protectors.
    • Visually and functionally inspect the gloves before use.
    • Wear the Insulation gloves with leather protectors at all times when working with the high voltage battery assembly, whether the system is energized or not.

Failure to follow the procedures may result in serious injury or death.

NOTE: 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.

Each device may need to be disconnected to isolate a circuit fault. Use the schematics and connector end views to identify the following:

  • High voltage energy management high speed GMLAN devices the vehicle is equipped with
  • High voltage energy management high speed GMLAN serial data circuit terminating resistors
  • Device locations on the high voltage energy management high speed GMLAN serial data circuits
  • Each device's ground, B+, ignition and high voltage energy management high speed GMLAN serial data circuit terminals
  1. Perform the High Voltage Disabling procedure before proceeding with this diagnostic. Refer to High Voltage Disabling .
  2. Reconnect the 12 V battery after performing the high voltage disabling procedure.
  3. Vehicle in Service Mode.
  4. Verify two or more devices are not communicating on the high voltage energy management 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 
  5. Vehicle OFF, all access doors closed, all vehicle systems OFF and all keys at least 3 m (9.8 ft) 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 min for all vehicle systems to power down.
  6. 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 
  7. Vehicle in Service Mode.
  8. Test for less than 4.5 V between the serial data circuits listed below and ground.
    • Terminal 3
    • Terminal 11
    • If less than 4.5 V 
  9. 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 2 min for all vehicle systems to power down.
  10. Test for greater than 100 Ω between the serial data circuits listed below and ground.
    • Terminal 3
    • Terminal 11
    • If greater than 100 Ω 
  11. Test for 50-70 Ω between the serial data circuit terminals 3 and 11.
    • 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 
  12. Refer to Testing the Device Circuits .
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