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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 control modules 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 control module for each of the following tests.

Each control module may need to be disconnected to isolate a circuit fault. Use the schematic to identify the following:

  • Control modules the vehicle is equipped with
  • High voltage energy management high speed GMLAN serial data circuit terminating resistors
  • Control module locations on the high voltage energy management high speed GMLAN serial data circuits
  • Each control module's 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. Disconnect the scan tool from the X84 data link connector (DLC). The following tests will be done at the X84B auxiliary data connector.
  4. Vehicle OFF and all vehicle systems OFF, all keys at least 3 meters away from vehicle, all access doors closed. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 10 Ω between the ground circuit terminal 5 and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  5. Vehicle in Service Mode, test for less than 4.5 V between the serial data circuits listed below and ground:
    • Terminal 3
    • Terminal 11
    • If greater than the specified range, test the serial data circuit for a short to voltage. Refer to Testing the Serial Data Circuits for a Short to Voltage.
  6. Vehicle OFF and all vehicle systems OFF, all keys at least 3 meters away from vehicle, all access doors closed. It may take up to 2 minutes for all vehicle systems to power down. Test for greater than 100 Ω between the serial data circuits listed below and ground:
    • Terminal 3
    • Terminal 11
    • If not the specified value, test the serial data circuit for a short to ground. Refer to Testing the Serial Data Circuits for a Short to Ground.
  7. Test for 50-70 Ω between the serial data circuits terminal 3 and terminal 11.
    • If less than 35 Ω, test for a short between the serial data circuits. Refer to Testing the Serial Data Circuits for a Short between the Circuits.
    • If 35-50 Ω there may be a third terminating resistor between the serial data circuits. This can happen if the incorrect control module is installed. Some control modules are available with and without the terminating resistors installed to reduce the need of terminating resistors in the wiring harness.
    • If greater than 70 Ω but less than infinite, test the serial data circuit for an open/high resistance. Refer to Testing the Serial Data Circuits for an Open/High Resistance.
    • If infinite, test the serial data circuits between the X84B auxiliary data connector and the first connection to the serial data circuit for an open/high resistance.
  8. If the serial data circuits test normal, refer to Testing the Control Module 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 control module.
  2. Vehicle in Service Mode, test for greater than 4.5 V between each serial data circuit at the control module connector that was just disconnected and ground. Verify that one or more serial data circuits are greater than 4.5 V.
    • If all serial data circuits are less than the specified range, replace the control module that was disconnected.
  3. Vehicle OFF, disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at another control module, in the direction of the circuit shorted to voltage.
  4. Vehicle in Service Mode, test for greater than 4.5 V between the serial data circuits at the control module connector that was just disconnected and ground. Verify that one or more serial data circuits are greater than 4.5 V.
    • If all serial data circuits are less than the specified range, replace the control module that was just disconnected.
  5. Repeat step 3 until one of the follow conditions are isolated:
    • A short to voltage on the serial data circuit between 2 control modules or splice packs, if equipped
    • A short to voltage on the serial data circuit between a control module and a terminating resistor

Testing the Serial Data Circuits for a Short to Ground

  1. Vehicle OFF, disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at an easily accessible control module.
  2. Vehicle OFF and all vehicle systems OFF, all keys at least 3 meters away from vehicle, all access doors closed. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 1k Ω between each serial data circuit at the control module connector that was just disconnected and ground. Verify that one or more serial data circuits are less than 1k Ω.
    • If all serial data circuits are greater than the specified range, replace the control module that was disconnected.
  3. Disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at another control module, in the direction of the circuit shorted to ground.
  4. Vehicle OFF and all vehicle systems OFF, all keys at least 3 meters away from vehicle, all access doors closed. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 1k Ω between the serial data circuits at the control module connector that was just disconnected and ground. Verify that one or more serial data circuits are less than 1k Ω.
    • If greater than the specified range for all serial data circuits, replace the control module that was just disconnected.
  5. Repeat step 3 until one of the follow conditions are isolated:
    • A short to ground on the serial data circuit between 2 control modules or splice packs, if equipped
    • A short to ground on the serial data circuit between a control module and a terminating resistor

Testing the Serial Data Circuits for a Short between the Circuits

  1. Vehicle OFF, disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at an easily accessible control module that is not communicating.
  2. Vehicle OFF and all vehicle systems OFF, all keys at least 3 meters away from vehicle, all access doors closed. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 110 Ω between each pair of serial data circuits at the control module connector that was just disconnected. Verify that one pair of serial data circuits are less than 110 Ω.
    • If each pair of serial data circuits is greater than the specified range, replace the control module that was disconnected.
  3. Connect the harness connectors at the control module that was disconnected.
  4. Disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at another control module, in the direction of the circuits shorted together.
  5. Vehicle OFF and all vehicle systems OFF, all keys at least 3 meters away from vehicle, all access doors closed. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 110 Ω between each pair of serial data circuits at the control module connector that was just disconnected. Verify that one pair of serial data circuits are less than 110 Ω.
    • If each pair of serial data circuits is greater than the specified range, replace the control module that was just disconnected.
  6. Repeat step 3 until one of the following conditions are isolated:
    • Serial data circuits shorted together between 2 control modules
    • Serial data circuits shorted together between a control module and a terminating resistor
    • A shorted terminating resistor

Testing the Serial Data Circuits for an Open/High Resistance

  1. Vehicle OFF, disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at an easily accessible control module that is not communicating.
  2. Vehicle OFF and all vehicle systems OFF, all keys at least 3 meters away from vehicle, all access doors closed. It may take up to 2 minutes for all vehicle systems to power down. Test for greater than 130 Ω between each pair of serial data circuits at the control module connector that was just disconnected. Verify that one pair of serial data circuits are greater than 130 Ω.
    • If each pair of serial data circuits is less than the specified range, replace the control module that was disconnected.
  3. Connect the harness connectors at the control module that was disconnected.
  4. Disconnect the harness connectors with the high voltage energy management high speed GMLAN serial data circuits at another control module, in the direction of the open circuit.
  5. Vehicle OFF and all vehicle systems OFF, all keys at least 3 meters away from vehicle, all access doors closed. It may take up to 2 minutes for all vehicle systems to power down. Test for greater than 130 Ω between each pair of serial data circuits at the control module connector that was just disconnected. Verify that one pair of serial data circuits is greater than 130 Ω.
    • If each pair of serial data circuits is less than the specified range, replace the control module that was just disconnected.
  6. Repeat step 3 until one of the following conditions are isolated:
    • An open/high resistance on the serial data circuit between 2 control modules
    • An open/high resistance on the serial data circuit between a control module and a terminating resistor
    • An open/high resistance terminating resistor

Testing the Control Module Circuits

  1. Vehicle OFF, disconnect the harness connectors at an easily accessible control module that is not communicating.
  2. Vehicle OFF and all vehicle systems OFF, all keys at least 3 meters away from vehicle, all access doors closed. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 10 Ω between each ground circuit terminal and ground, at the control module connector that was just disconnected.
    • If greater than the specified range, test the ground circuit and ground connection for an open/high resistance.
  3. Vehicle OFF, verify that a test lamp does not illuminate between each ignition circuit terminal and ground.
    • If the test lamp does illuminate, test the ignition circuit for a short to voltage. If the circuits test normal, replace the appropriate control module.
  4. Vehicle in Service Mode, verify that a test lamp illuminates between each ignition circuit terminal and ground.
    • If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuits test normal, replace the appropriate control module.
  5. Vehicle OFF, connect the harness connectors at the control module that was disconnected.
  6. Repeat step 1 at another control module that is not communicating until one of the following conditions are isolated:
    • An open/high resistance on the ground circuit or ground connection
    • A short to voltage, a short to ground, or an open/high resistance on the ignition circuit
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