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Circuit/System Testing

NOTE:

Use the Wiring Schematics and connector end views to identify the device's ground, B+, ignition, accessory wakeup serial data, and serial data circuit terminals.

  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 connector at the T19 Power Supply Transformer. It may take up to 10 min for all vehicle systems to power down.
  2. Test for less than 10 Ω between each ground circuit terminal 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.
    • Go to next step: If less than 10 Ω 
    3. NOTE:

    If equipped with S38 Ignition Mode Switch (RPO BTM), the vehicle will not power up after the T19 Power Supply Transformer is disconnected. Unplug the connector with the ignition on/vehicle in service mode. Verify the malfunction indicator lamp is illuminated on the driver information center after disconnecting the connector to verify the vehicle is still powered up.

  3. Ignition ON/Vehicle In Service Mode, verify the vehicle is not equipped with S38 Ignition Mode Switch (RPO BTM).
    • If the vehicle is equipped with S38 Ignition Mode Switch 
    1. Reconnect the harness connector at T19 Power Supply Transformer.
    2. Ignition ON/Vehicle In Service Mode.
    3. Disconnect the harness connector at T19 Power Supply Transformer with the ignition still on.
    4. Proceed to step 4.
    • Go to next step: If the vehicle is not equipped with S38 Ignition Mode Switch 
  4. 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 T19 Power Supply Transformer.
    • Go to next step: If the test lamp illuminates 
  5. If equipped, verify a test lamp illuminates between each ignition 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 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 T19 Power Supply Transformer.
    • Go to next step: If the test lamp illuminates 
  6. If equipped, verify a test lamp illuminates between the accessory wakeup serial data circuit terminal and ground.
    • If the test lamp does not illuminate 
    1. Ignition/Vehicle OFF, remove the test lamp, disconnect the harness connectors at the K9 Body Control Module.
    2. Test for less than 2 Ω in the accessory wakeup serial data circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K9 Body Control Module.
    • Go to next step: If the test lamp illuminates 
  7. Test for less than 4.5 V between each powertrain high speed GMLAN serial data circuit terminal and ground.
    • Go to next step: If less than 4.5 V 
  8. 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 10 min for all vehicle systems to power down.
  9. Test for greater than 100 Ω between each powertrain high speed GMLAN serial data circuit terminal and ground.
    • Go to next step: If greater than 100 Ω 
  10. Disconnect the harness connectors at the device setting the DTC.
  11. Test for less than 2 Ω in each powertrain high speed GMLAN serial data circuits end to end between the T19 Power Supply Transformer and the device setting the DTC.
    • If 2 Ω or greater 

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

    • Go to next step: If less than 2 Ω 
  12. Replace the T19 Power Supply Transformer.
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