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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 High 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. Ignition OFF, disconnect the harness connector of the BCM.
  2. Ignition ON, test for battery voltage between each voltage input circuit of the BCM and ground.
    • If less than battery voltage, test each voltage output circuit of the BCM for a short to ground, and each voltage input circuit of the BCM for a short to ground or and open/high resistance. If the circuits test normal, replace the faulty module.
  3. Test for less than 1 ohm of resistance between each ground circuit of the BCM and ground.
    • If greater than 1 ohm, repair the ground circuit for an open/high resistance.
  4. Disconnect the vehicle communication interface module (VCIM) connector if equipped with UE1, or terminator resistor connector if not equipped with UE1.
  5. Test for less than 1.0 volt between the high speed GMLAN serial data circuits of the DLC and ground.
    • If greater than 1.0 volt, repair the serial data circuit for a short to voltage.
  6. Test for infinite resistance between the high speed GMLAN serial data circuit of the DLC and ground.
    • If less than infinite resistance, repair the serial data circuit for a short to ground.
  7. Test for infinite resistance between the high speed GMLAN serial data (+) and (-) circuits of the DLC.
    • If less than infinite resistance, repair the serial data circuits for a short between them.
  8. Reconnect the BCM harness connector.
  9. Attempt to communicate with the BCM. Communication should not be available.
    • If equipped with UE1, test between the high speed GMLAN serial data (+) and (-) circuits of the terminator resistor for 120 ohm resistance. If the circuit tests normal, replace the VCIM.
    • If not equipped with UE1, replace the terminator resistor.
  10. Beginning with the farthest module from the DLC that is connected to high speed GMLAN serial data circuits, disconnect each module one at a time, attempting to communicate with the BCM after each disconnect. Communications should not be available.
    • If furthest module was the last module disconnected, replace the faulty module.
    • If more than one module was disconnected, test the high speed GMLAN serial data (+) and (-) circuits between the last two disconnected modules for a short to voltage, short to ground or a short between them. If the circuits test normal, replace the last disconnected module.
  11. Test the high speed GMLAN serial data (+) and (-) circuits between the BCM and the last disconnected module for a short to voltage, short to ground or a short between them. If the circuits test normal, replace the BCM.
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