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Home >> Cadillac >> 2007 >> Escalade EXT >> Repair and Diagnosis >> External Pages >> Different car >> Section 1607 (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 2010 GMC Sierra, 2010 GMC Cab & Chassis Sierra, 2010 Chevrolet Silverado, and 2010 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
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-U02FF (with HP2)  or DTC U0100-U02FF (without HP2) .
    • If one or more control modules are communicating but not all, refer to Testing the Serial Data Circuit for an Open/High Resistance.
  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.
  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.
  6. Disconnect the harness connector at the JX 221 splice pack.
  7. Test for less than 2 Ω between the serial data circuit terminal 1 and the JX 221 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 221, JX 339, and JX 223 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 221, JX 339, and JX 223 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 339 splice pack, ignition ON, verify the scan tool communicates with one or more control modules connected to the JX 339 splice pack.
    • If all control modules on the JX 339 spice pack do not communicate, test the serial data circuit between the JX 221 and JX 339 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 221 if the control modules not communicating are connected to the JX 221 splice pack
    • JX 223 if the control modules not communicating are connected to the JX 223 splice pack, if equipped
    • JX 339 if the control modules not communicating are connected to the JX 339 splice pack
  3. Install a 3A fused jumper wire between the disconnected splice pack connector terminal listed below and a low speed GMLAN serial data circuit that is not communicating:
    • JX 221 terminal D
    • JX 223 terminal A
    • JX 339 terminal A
  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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