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Circuit/System Testing

  1. Ignition OFF, disconnect the harness connector at the low speed splice pack.
  2. Ignition ON, test for less than 1.0 volt between the low speed GMLAN serial data circuit of the DLC and ground.
    • If greater than 1.0 volt, repair the serial data circuit for a short to voltage.
  3. Test for infinite resistance between the serial data circuit of the DLC and ground.
    • If less than infinite resistance, repair the serial data circuit for a short to ground.
  4. Test for less than 1.0 ohm of resistance in the serial data circuit between the DLC and the splice pack.
    • If greater than 1.0 ohm, repair the serial data circuit for an open/high resistance.
  5. Install a 3-amp fused jumper wire between pin A and pin M of the splice pack. Install another 3-amp fused jumper wire to pin M.
  6. Using the extra jumper wire from pin M attempt to establish communications with any other module connected to the splice pack. At least one module should be able to communicate.
    • If communications can't be established with any module, test the serial data circuit of the BCM for a short to voltage, short to ground or open/high resistance. If the circuit tests normal, replace the BCM.
  7. Using the extra jumper wire at pin M, continue testing each serial data circuit at the splice pack for communications. All modules should be able to communicate.
    • If there is only one module connected, test the serial data circuit for a short to voltage or a short to ground. If the circuit tests normal, replace the faulty module.
    • If there are multiple modules, test each serial data circuit for a short to voltage or a short to ground, with the modules disconnected. If the circuit tests normal, install each module one at a time starting with the closest module to the splice pack until communications stop. Replace the faulty module.
  8. If all circuits test normal, test or replace the splice pack.
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