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Circuit/System Testing

NOTE:

Use the schematic to identify the following:

  • Gateway Isolated low speed GMLAN devices the vehicle is equipped with
  • Device and splice pack locations on the gateway isolated low speed GMLAN serial data circuit
  • The gateway isolated low speed GMLAN serial data circuit terminals for each device or splice pack
  1. Ignition/Vehicle OFF, disconnect the appropriate harness connectors at all gateway isolated low speed GMLAN serial data splice packs, ignition ON/Vehicle In Service Mode.
  2. Test for less than 4.5 V between each gateway isolated low speed GMLAN serial data circuit at a splice pack and ground.
    • If any serial data circuit is greater than 4.5 V 
    1. Ignition/Vehicle OFF, disconnect all devices on the failed serial data circuit, ignition ON/Vehicle In Service Mode.
    2. Test for less than 1 V between each section of the failed serial data circuit and ground.
      • If 1 V or greater, repair the short to voltage in the circuit.
      • If less than 1 V
    3. Connect the splice pack and connect the first device on the failed serial data circuit, ignition ON/Vehicle In Service Mode.
    4. Verify the scan tool communicates or not with the gateway isolated low speed GMLAN serial data circuit.
      • If the scan tool does not communicate, replace the device that was just connected.
      • If the scan tool communicates and there are more devices to connect, connect the next device and repeat step 2.4.
      • If the scan tool communicates and there are no more devices to connect
    5. All OK.
    • If all serial data circuits are less than 4.5 V 
  3. 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 appropriate harness connectors at all gateway isolated low speed GMLAN serial data splice packs. It may take up to 2 min for all vehicle systems to power down.
  4. Test for greater than 100 Ω between each gateway isolated low speed GMLAN serial data circuit at a splice pack and ground.
    • If any serial data circuit is 100 Ω or less 
    1. Disconnect all devices on the failed serial data circuit.
    2. Test for infinite resistance between each section of the failed serial data circuit and ground.
      • If less than infinite resistance, repair the short to ground in the circuit.
      • If infinite resistance
    3. Connect the splice pack and connect the first device on the failed serial data circuit, ignition ON/Vehicle In Service Mode.
    4. Verify the scan tool communicates or not with the gateway isolated low speed GMLAN serial data circuit.
      • If the scan tool does not communicate, replace the device that was just connected.
      • If the scan tool communicates and there are more devices to connect, connect the next device and repeat step 4.4.
      • If the scan tool communicates and there are no more devices to connect
    5. All OK.
    • If all serial data circuits are greater than 100 Ω 
  5. Inspect all gateway isolated low speed GMLAN splice packs for damage.

Testing the Serial Data Circuit 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. Disconnect the harness connectors at the gateway isolated low speed GMLAN device that is not communicating and closest to the K56 Serial Data Gateway Module.
  3. Disconnect the harness connectors at the K56 Serial Data Gateway Module.
  4. Test for less than 2 Ω in the gateway isolated low speed GMLAN serial data circuit (circuit number 1102) 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 
  5. Test for less than 2 Ω in the primary low speed GMLAN serial data circuit (circuit number 5060) end to end between the K56 Serial Data Gateway Module and the X84 Data Link Connector terminal 1.
    • If 2 Ω or greater 

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

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

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. Disconnect the harness connectors at the Gateway isolated low speed GMLAN device that is not communicating. 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 isolated low 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 the primary low speed GMLAN serial data circuit (circuit number 5060) end to end between the K56 Serial Data Gateway Module and X84 Data Link Connector terminal 1.
    • If 2 Ω or greater 

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

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