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Home >> Saturn >> 2007 >> Relay 3.9 1 >> Repair and Diagnosis >> External Pages >> Different car >> Section 129 (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

WARNING: This page is about a different car, the 2007 Chevrolet Monte Carlo and 2007 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.
  1. Test for less than 1 ohm of resistance between the DLC ground circuit terminal 5 and ground.
    • If greater than 1 ohm, test the ground circuit for open/high resistance.
  2. Ignition OFF, disconnect the harness connector (splice pack comb) at SP 205. Install a 3-amp fused jumper wire between pin A and pin M of SP 205, harness side.
  3. Ignition ON, with a scan tool, attempt to communicate with the BCM. Communication should be available.
    • If no communication, test the following circuits: serial data circuit for a short to ground, a short to voltage or an open/high resistance between the BCM and DLC, BCM voltage inputs for open/high resistance or short to ground, BCM grounds for open/high resistance. If the circuits test normal, replace the BCM.
  4. Install another 3-amp fused jumper wire to pin A of SP 205, harness side.
  5. Use the other end of the jumper wire to connect all other pins, harness side, one at a time and verify that low speed communication remains available to the BCM.
    • If low speed communication is interrupted after connecting an individual module at SP 205, test the serial data circuit between SP 205 and the last module connected for a short to ground and short to voltage. If the circuit tests normal, replace the module that caused no communication.
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