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Circuit/System Testing

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 only one device is not communicating 

      Refer to Testing the Device Circuits.

    • 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 4.5 V or greater 

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

    • 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 100 Ω or less 

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

    • If greater than 100 Ω 
  11. Test for 50-70 Ω between the serial data circuit terminals 3 and 11.
    • If less than 35 Ω 

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

    • 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 greater than 70 Ω but less than infinite 

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

    • 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.

Testing the Serial Data Circuits for a Short to Voltage

  1. Vehicle OFF, disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at an easily accessible device, Vehicle in Service Mode.
  2. Test for greater than 4.5 V between each serial data circuit at the device connector that was just disconnected and ground.
    • If each serial data circuit is 4.5 V or less 
    1. Vehicle OFF.
    2. Test for less than 10 Ω between each of the device's ground circuit terminals and ground.
      • If 10 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 10 Ω, replace the device that was disconnected.
    • If any serial data circuit is greater than 4.5 V 
  3. Vehicle OFF, disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted to voltage, Vehicle in Service Mode.
  4. Test for greater than 4.5 V between each serial data circuit at the device connector that was just disconnected and ground.
    • If each serial data circuit is 4.5 V or less 
    1. Vehicle OFF.
    2. Test for less than 10 Ω between each of the device's ground circuit terminals and ground.
      • If 10 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 10 Ω, replace the device that was disconnected.
    • If any serial data circuit is greater than 4.5 V 
  5. Repeat step 3 until one of the following conditions are isolated:
    • A short to voltage on the serial data circuit between two devices or splice packs, if equipped.
    • A short to voltage on the serial data circuit between a device and a terminating resistor.

Testing the Serial Data Circuits for a Short to Ground

  1. 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.
  2. Disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at an easily accessible device.
  3. Test for greater than 100 Ω between each serial data circuit at the device connector that was just disconnected and ground.
    • If each serial data circuit is 100 Ω or greater 

      Replace the device that was disconnected.

    • If any serial data circuit is less than 100 Ω 
  4. Disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted to ground.
  5. Test for greater than 100 Ω between each serial data circuit at the device connector that was just disconnected and ground.
    • If both serial data circuits are 100 Ω or greater 

      Replace the device that was disconnected.

    • If any serial data circuit is less than 100 Ω 
  6. Repeat step 4 until one of the following conditions are isolated:
    • A short to ground on the serial data circuit between two devices or splice packs, if equipped.
    • A short to ground on the serial data circuit between a device and a terminating resistor.
    • A short to ground on the serial data circuit between the X84B Auxiliary Data Connector and the first device or splice pack.

Testing the Serial Data Circuits for a Short between the Circuits

  1. 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.
  2. Disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at an easily accessible device that is not communicating.
  3. Test for greater than 110 Ω between each pair of serial data circuits at the device connector that was just disconnected.
    • If each pair of serial data circuits is 110 Ω or greater 

      Replace the device that was disconnected.

    • If any pair of serial data circuits is less than 110 Ω 
  4. Connect the harness connectors at the device that was disconnected.
  5. Disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted together.
  6. Test for greater than 110 Ω between each pair of serial data circuits at the device connector that was just disconnected.
    • If each pair of serial data circuits is 110 Ω or greater 

      Replace the device that was disconnected.

    • If any pair of serial data circuits is less than 110 Ω 
  7. Repeat step 4 until one of the following conditions are isolated:
    • Serial data circuits shorted together between two devices or splice packs, if equipped.
    • Serial data circuits shorted together between a device and a terminating resistor.
    • Serial data circuits shorted together between the X84B Auxiliary Data Connector and the first device or splice pack.
    • A shorted terminating resistor.

Testing the Serial Data Circuits for an Open/High Resistance

  1. 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.
  2. Disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at an easily accessible device that is not communicating.
  3. Test for less than 130 Ω between each pair of serial data circuits at the device connector that was just disconnected.
    • If each pair of serial data circuit is 130 Ω or less 

      Replace the device that was disconnected.

    • If any pair of serial data circuits is greater than 130 Ω 
  4. Connect the harness connectors at the device that was disconnected.
  5. Disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at another device, in the direction of the circuit with the open/high resistance.
  6. Test for less than 130 Ω between each pair of serial data circuits at the device connector that was just disconnected.
    • If each pair of serial data circuits is 130 Ω or less 

      Replace the device that was disconnected.

    • If any pair of serial data circuits is greater than 130 Ω 
  7. Repeat step 4 until one of the following conditions are isolated:
    • An open/high resistance on the serial data circuit between two devices or splice packs, if equipped.
    • An open/high resistance on the serial data circuit between a device and a terminating resistor.
    • An open/high resistance terminating resistor.

Testing the Device Circuits

  1. 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.
  2. Disconnect the harness connectors at an easily accessible device that is not communicating.
  3. Test for less than 10 Ω between each ground circuit terminal 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 
  4. Vehicle in Service Mode
  5. If equipped, 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. Vehicle OFF.
    2. Test for less than 2 Ω in the B+ circuit end to end.
      • If 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. Vehicle OFF.
    2. Test for infinite resistance between the B+ circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the disconnected device.
    • If the test lamp illuminates 
  6. Vehicle in Service Mode.
  7. If equipped, verify a test lamp illuminates between each ignition circuit terminal, which has a fuse in the circuit, and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Vehicle OFF.
    2. Test for less than 2 Ω in the ignition circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Vehicle OFF.
    2. Test for infinite resistance between the ignition circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the disconnected device.
    • If the test lamp illuminates 
  8. Vehicle in Service Mode
  9. If equipped, verify a test lamp illuminates between each ignition circuit terminal, which is controlled by a control module, and ground.
    • If the test lamp does not illuminate 
    1. Vehicle OFF, disconnect the harness connectors at the control module that controls the ignition circuit.
    2. Test for infinite resistance between the ignition circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance
    3. Test for less than 2 Ω in the ignition circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the control module that controls the ignition circuit.
    • If the test lamp illuminates 
  10. 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.
  11. Test for less than 130 Ω between each pair of high voltage energy management high speed GMLAN serial data circuits at the device connector that was just disconnected.
    • If any pair of serial data circuits is greater than 130 Ω 

      Repair the open/high resistance in the serial data circuits between the disconnected device and the circuit splice in the serial data circuits.

    • If each pair of serial data circuits is 130 Ω or less 
  12. Replace the device that was disconnected.
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