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Circuit/System Testing

NOTE:

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

  • Gateway expansion high speed GMLAN devices and terminating resistors the vehicle is equipped with
  • Device locations on the gateway expansion high speed GMLAN serial data circuits
  • Each device's ground, B+, ignition, and gateway expansion high speed GMLAN serial data circuit terminals

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.

  1. Ignition/Vehicle OFF, disconnect the harness connectors with the gateway expansion high speed GMLAN serial data circuits at an easily accessible device that is not communicating. Refer to Data Link References  to determine which devices are on the gateway expansion high speed GMLAN bus.
  2. Ignition ON/Vehicle In Service Mode.
  3. Test for less than 4.5 V between each gateway expansion high speed GMLAN serial data circuit at the device that was just disconnected and ground.
    • If 4.5 V or greater 

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

    • If less than 4.5 V 
  4. Ignition/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.
  5. Test for greater than 100 Ω between each gateway expansion high speed GMLAN serial data circuit at the device that was just disconnected and ground.
    • If 100 Ω or less 

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

    • If greater than 100 Ω 
  6. Test for 110 - 130 Ω between each pair of the gateway expansion 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.

    • If between 110 - 130 Ω 
  7. Refer to Testing the Device Circuits.

Testing the Serial Data Circuits for a Short to Voltage

  1. Ignition/Vehicle OFF, disconnect the harness connectors with the gateway expansion high speed GMLAN serial data circuits at another device, in the direction of the circuit shorted to voltage, ignition ON/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. Ignition/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. 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. Ignition/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 gateway expansion 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 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. Repeat step 1 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. Ignition/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 with the gateway expansion 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.

    • 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. Ignition/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 with the gateway expansion 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 the 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 
  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. Ignition/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. Ignition/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 
  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. Ignition/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. Ignition/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.
    • If the test lamp illuminates 
  4. Ignition ON/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. Ignition/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. Ignition/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.
    • 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. Ignition/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.
      • 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 
  7. Ignition/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 harness connectors at the K56 Serial Data Gateway Module. It may take up to 2 min for all vehicle systems to power down.
  8. Test for less than 2 Ω in each of the gateway expansion high speed GMLAN serial data circuits end to end between the non communicating device and the K56 Serial Data Gateway Module.
    • If 2 Ω or greater 

      Repair the open/high resistance in the serial data circuit.

    • If less than 2 Ω 
  9. Test for less than 2 Ω in each of the primary high speed GMLAN serial data circuits (circuit numbers 2500 & 2501) end to end between the K56 Serial Data Gateway Module and the appropriate X84 Data Link Connector (DLC) terminals listed below.
    • X84 Data Link Connector high speed GMLAN serial data circuit terminal 6
    • X84 Data Link Connector high speed GMLAN serial data circuit terminal 14
    • If 2 Ω or greater 

      Repair the open/high resistance in the high speed GMLAN serial data circuit.

    • If less than 2 Ω 
  10. Replace the non communicating device that was disconnected.
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