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Circuit/System Testing: Notes

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.
      • Go to next step: 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.
      • Go to next step: If the scan tool communicates and there are no more devices to connect
    5. All OK.
    • Go to next step: 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.
      • Go to next step: 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.
      • Go to next step: If the scan tool communicates and there are no more devices to connect
    5. All OK.
    • Go to next step: If all serial data circuits are greater than 100 Ω 
  5. Inspect all gateway isolated low speed GMLAN splice packs for damage.
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