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Home >> Cadillac >> 2018 >> CT6 Plug-In >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Data Communication System - Diagnostic Information And Procedures (B1000-U1833) >> Diagnostic Information and Procedures >> DTC U007A >> Circuit/System Testing
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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 and terminating resistors the vehicle is equipped with
  • 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. Refer to Data Link References to determine which devices are on the high voltage energy management expansion bus.
  4. 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. Disconnect the harness connectors containing the high voltage energy management high speed GMLAN serial data circuits at an easily accessible device that is not communicating.
  5. Vehicle in Service Mode.
  6. Test for less than 4.5 V between each high voltage energy management high speed GMLAN serial data circuit at the device that was just disconnected and ground.
    • If any serial data circuit is 4.5 V or greater 

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

    • Go to next step: If all serial data circuits are less than 4.5 V 
  7. 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.
  8. Test for greater than 100 Ω between each high voltage energy management high speed GMLAN serial data circuit at the device that was just disconnected and ground.
    • If any serial data circuit is 100 Ω or less 

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

    • Go to next step: If all serial data circuits are greater than 100 Ω 
  9. Test for 110 - 130 Ω between each pair of the high voltage energy management high speed GMLAN 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.

    • Go to next step: If between 110 - 130 Ω 
  10. Refer to Testing the Device Circuits.

Testing the Serial Data Circuits for a Short to Voltage

  1. Vehicle OFF, disconnect the harness connectors containing 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.
  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, 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. 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.
    • Go to next step: If any serial data circuit is greater than 4.5 V 
  3. Repeat step 1 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 containing the high voltage energy management high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted to ground.
  3. Test for greater than 100 Ω between each serial data circuit at the device connector that was just disconnected and ground.
    • If all serial data circuits are 100 Ω or greater 

      Replace the device that was disconnected.

    • Go to next step: If any serial data circuit is less than 100 Ω 
  4. Repeat step 2 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.

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. Connect the harness connectors at the device that was previously disconnected.
  3. Disconnect the harness connectors containing the high voltage energy management high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted together.
  4. 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.

    • Go to next step: If any pair of serial data circuits is less than 110 Ω 
  5. Repeat step 2 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.
    • 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. Connect the harness connectors at the device that was previously disconnected.
  3. Disconnect the harness connectors containing 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.
  4. 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.

    • Go to next step: If any pair of serial data circuits is greater than 130 Ω 
  5. Repeat step 2 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. Test for less than 10 Ω between each ground circuit terminal at the device that was just disconnected 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.
    • Go to next step: If less than 10 Ω 
  3. 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, remove the test lamp.
    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, remove the test lamp.
    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.
    • Go to next step: If the test lamp illuminates 
  4. Vehicle in Service Mode.
  5. 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, remove the test lamp.
    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, remove the test lamp.
    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.
    • Go to next step: If the test lamp illuminates 
  6. 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, remove the test lamp, 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.
      • Go to next step: 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.
    • Go to next step: If the test lamp illuminates 
  7. Replace the device that was disconnected.
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