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Home >> Cadillac >> 2007 >> Escalade EXT >> Repair and Diagnosis >> External Pages >> Different car >> Section 1184 (Data Communication System) >> Diagnostic Information and Procedures >> Scan Tool Does Not Communicate with Low Speed GMLAN Device >> JX 405 Circuit Test
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JX 405 Circuit Test

WARNING: This page is about a different car, the 2008 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, remove the scan tool from the DLC, and disconnect the harness connector at JX 405.
  2. Ignition ON, test for less than 1 volt between serial data circuit terminal 1 of JX 405 and ground.
    • If greater than the specified range, test the serial data circuit for a short to voltage.
  3. Test for infinite resistance between the serial data circuit terminal 1 of JX 405 and ground.
    • If less than the specified value, test the serial data circuit for a short to ground.
  4. Disconnect the fused jumper from JX 205 terminal 2, and connect to terminal 12. Install another 3-amp fused jumper wire to terminal 1 of JX 205.
  5. Establish communications with the BCM.
    6. IMPORTANT: Allow communications for 5 seconds after connecting a module with the jumper to determine if communication is interrupted or not.
  6. With BCM communications established, use the other end of the jumper wire to connect the JX 405 terminals listed, one at a time and verify that low speed communication remains available to the BCM.
    • 4 - RPO UK8
    • 6
    • 7 - RPO UD7
    • 8 - RPO UE1
    • 9 - RPO U2K
    • 11 - RPO E61
    • 12 - RPO A45 or KA1
    • If communication is interrupted after connecting an individual module at JX 405, test the serial data circuit between JX 405 and the last module connected for a short to voltage or short to ground. If the circuit tests normal, replace the module that caused no communication.
  7. Disconnect the harness connector at the rollover sensor.
  8. Connect the open end of the fused jumper wire to the serial data circuit terminal 10 of JX 405 and attempt to communicate with the BCM. Communication should not be available.
    • If communication is available, replace the rollover sensor.
  9. Ignition OFF, disconnect the harness connector at the passenger presence system (PPS) module, and attempt to communicate with the BCM. Communication should not be available.
    • If communication is available, test the serial data circuit between the PPS and the rollover sensor for a short to voltage or short to ground. If the circuit tests normal, replace the PPS module.
  10. Ignition OFF, disconnect the harness connector at the inflatable restraint sensing and diagnostic module (SDM), and attempt to communicate with the BCM. Communication should not be available.
    • If communication is available, test the serial data circuit between the SDM and the PPS module for a short to voltage or short to ground. If the circuit tests normal, replace the SDM.
  11. Test the serial data circuit between the SDM and the PPS module for a short to voltage or short to ground.
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