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Home >> Cadillac >> 2009 >> Escalade EXT >> 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

NOTE: Use the schematic to identify the following:
  • Control modules the vehicle is equipped with
  • Control module locations on the low speed GMLAN serial data circuit
  • Each control module's low speed GMLAN serial data circuit terminals
  1. Attempt to communicate with all control modules on the low speed GMLAN serial data circuit, refer to Data Link References . Communications should not be available with two or more control modules on the low speed GMLAN serial data circuit.
    • If only one control module is not communicating, diagnose that control module only, refer to DTC U0100-U0299 .
    • If one or more control modules are communicating but not all, refer to Testing the Serial Data Circuit for an Open/High Resistance below.
  2. Disconnect the scan tool from the DLC. The following tests will be done at the DLC connector.
  3. All access doors closed, ignition OFF for 60 seconds, test for less than 10 Ω between the ground circuit terminal 5 and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  4. Ignition ON, test for less than 4.5 V between the serial data circuit terminal 1 and ground.
    • If greater than the specified range, test the serial data circuit for a short to voltage, refer to Testing the Serial Data Circuit for a Short to Voltage below.
  5. Ignition OFF for 60 seconds, test for greater than 100 Ω between the serial data circuit terminal 1 and ground.
    • If not the specified value, test the serial data circuit for a short to ground, refer to Testing the Serial Data Circuits for a Short to ground below.
  6. Disconnect the harness connector at the JX 200 splice pack.
  7. Test for less than 2 Ω between the serial data circuit terminal 1 and the JX 200 splice pack terminal D.
    • If greater than the specified range, test the serial data circuit for an open/high resistance. If the circuits test normal, replace the splice pack.

Testing the Serial Data Circuits for a Short to Voltage

  1. Ignition OFF, disconnect the harness connectors at the JX 200, JX 300, and JX 201 splice packs, as equipped.
  2. Ignition ON, test for less than 4.5 V between the DLC serial data circuit terminal 1 and ground.
    • If greater than the specified range, repair the short to voltage.
  3. Test for less than 4.5 V between each serial data circuit and ground.
    • If greater than the specified range, perform the appropriate test listed below:

Testing the Serial Data Circuits for a Short to Ground

  1. Ignition OFF, disconnect the harness connectors at the JX 200, JX 300, and JX 201 splice packs, as equipped.
  2. Test for infinite resistance between the DLC serial data circuit terminal 1 and ground.
    • If not the specified value, repair the short to ground.
  3. Ignition OFF for 60 seconds, test for greater than 100 Ω between each serial data circuit and ground.
    • If less than the specified range, perform the appropriate test listed below:

Testing the Serial Data Circuit for an Open/High Resistance

  1. If equipped with a JX 300 splice pack, ignition ON, verify the scan tool communicates with one or more control modules connected to the JX 300 splice pack.
    • If all control modules on the JX 300 spice pack do not communicate, test the serial data circuit between the JX 200 and JX 300 splice packs for an open/high resistance. If the circuit tests normal, test each splice pack for an open/high resistance.
  2. Ignition OFF, disconnect one of the harness connectors listed below:
    • JX 200 if the control modules not communicating are connected to the JX 200 splice pack
    • JX 201 if the control modules not communicating are connected to the JX 201 splice pack, if equipped
    • JX 300 if the control modules not communicating are connected to the JX 300 splice pack
  3. Install a 3A fused jumper wire between the disconnected splice pack terminal 1 and a low speed GMLAN serial data circuit that is not communicating.
  4. Ignition ON, verify the scan tool communicates with the control modules connected to the low speed GMLAN serial data circuit.
    • If any control module does not communicate, test each section of the serial data circuit for an open/high resistance. If the circuits test normal, replace the control module that does not communicate when connected.
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