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Home >> Chevrolet >> 2014 >> SS >> Repair and Diagnosis >> Engine Performance >> System >> Data Communication System >> Diagnostic Information and Procedures >> Scan Tool Does Not Communicate with Low Speed GMLAN Device >> Circuit/System Testing
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Circuit/System Testing

Testing the Serial Data Circuits for a Short to Voltage

  1. Ignition OFF, disconnect the appropriate harness connectors at all low speed GMLAN serial data splice packs, ignition ON.
  2. Test for less than 4.5 V between the serial data circuit terminal 1 at the X84 Data Link Connector and ground.
    • If 4.5 V or greater 

      Repair the short to voltage on the serial data circuit.

    • If less than 4.5 V 
  3. Test for less than 4.5 V between each 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 OFF, disconnect all devices on the failed serial data circuit, ignition ON.
    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.
    4. Verify the scan tool communicates or not with the 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 3.4.
      • 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 
  4. All OK.

Testing the Serial Data Circuits for a Short to Ground

  1. Ignition 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 low speed GMLAN serial data splice packs.
  2. Test for infinite resistance between the serial data circuit terminal 1 at the X84 Data Link Connector and ground.
    • If less than infinite resistance 

      Repair the short to ground on the serial data circuit.

    • If infinite resistance 
  3. Test for greater than 100 Ω between each 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.
    4. Verify the scan tool communicates or not with the 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 3.4.
      • 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 
  4. All OK.

Testing the Serial Data Circuit for an Open/High Resistance

  1. Ignition OFF and all vehicle systems OFF, disconnect the splice pack containing the devices that are not communicating on the low speed GMLAN serial data circuit.
  2. Test for less than 2 Ω between the X84 Data Link Connector terminal 1 and the disconnected splice pack.
    • If 2 Ω or greater 

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

    • If less than 2 Ω 
  3. Disconnect all devices on the failed serial data circuit.
  4. Test for less than 2 Ω between each section of the failed serial data circuit end to end.
    • If 2 Ω or greater 

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

    • If less than 2 Ω 
  5. Connect the splice pack and connect the first device on the failed serial data circuit.
  6. Verify if the device communicates or not with the scan tool.
    • If the device does not communicates 

      Replace the device.

    • If the device communicates and there are more devices to connect 

      Connect the next device on the failed serial data circuit and repeat step 6.

    • If all devices are connected and communicating 
  7. All OK.
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