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Home >> Isuzu >> 2007 >> Ascender RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 307 (Data Communication System) >> Diagnostic Information & Procedures >> Scan Tool Does Not Communicate with Class 2 Device >> Circuit/System Testing
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Circuit/System Testing

WARNING: This page is about a different car, the 2008 Isuzu Ascender, 2008 GMC Envoy, and 2008 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.

Class 2 Communication Initial Test 

  1. Test for less than 1 ohm between the DLC ground circuit terminal 5 and ground.
    • If greater than the specified range, test the ground circuit for open/high resistance.
  2. Ignition OFF, disconnect the harness connector of JX305 and attempt to communicate with the BCM. Communication should not be available.
    • If communication is available, refer to JX305 Test.
  3. Ignition OFF, disconnect the harness connector of JX205.
  4. Ignition ON, test for less than 1 volt between the serial data circuit terminal H of JX205 and ground.
    • If greater than the specified range, test the serial data circuit for a short to voltage.
  5. Test for infinite resistance between the serial data circuit terminal H of JX205 and ground.
    • If less than the specified value, test the serial data circuit for a short to ground.
  6. Ignition ON, test for less than 1 volt between the serial data circuit terminal A of JX205 and ground.
    • If greater than the specified range, test the serial data circuit for a short to voltage.
  7. Test for infinite resistance between the serial data circuit terminal A of JX205 and ground.
    • If less than the specified value, test the serial data circuit for a short to ground.
  8. Test for less than 1 ohm on the serial data circuit between terminal A of JX205 and terminal 2 of the DLC.
    • If greater than the specified range, test the serial data circuit for open/high resistance.
  9. Ignition OFF, disconnect the harness connectors X1 and X3 of the BCM
  10. Verify a test lamp illuminates between each ground circuit terminal of the BCM listed below and B+.
    • X3 - A11
    • X3 - B11
    • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  11. Ignition ON, verify a test lamp illuminates between each voltage circuit terminal of the BCM listed below and ground.
    • X1 - A3
    • X1 - A19
    • X3 - A1
    • X3 - A2
    • X3 - A20
    • X3 - B4
    • X3 - B13
    • X3 - B15
    • X3 - B17
    • X3 - B18
    • If the test lamp does not illuminate, test the voltage circuit for an open/high resistance or short to ground.
  12. Ignition OFF, connect the harness connectors of the BCM.
  13. Ignition OFF, connect a 3-amp fused jumper wire between terminal A and terminal M of JX205. Attempt to communicate with the BCM. Communication should be available.
    • If communication is not available, test the serial data circuit for a short to voltage, or short to ground between the BCM and JX205. If the circuits test normal, replace the BCM.
    14. IMPORTANT: After each connection, wait for 5 seconds to determine that communication remains available.
  14. Connect another 3-amp fused jumper wire to terminal A of JX205. Individually connect the other end of the jumper wire to each other terminal of JX205 and verify that communication remains available to the BCM.
    • If communication is interrupted, test the serial data circuit between JX205 and the last module connected for a short to ground or a short to voltage. If the circuit tests normal, replace the module that caused no communication.

JX305 Test 

  1. Ignition OFF, connect a 3-amp fused jumper wire to terminal M of JX305.
    2. IMPORTANT: After each connection, wait for 5 seconds to determine that communication remains available.
  2. While communicating with the BCM, individually move the other end of the jumper wire to each of the terminals of JX305 and verify that communication remains available to the BCM.
    • If communication is interrupted, test the serial data circuit between JX305 and the last module connected for a short to ground or a short to voltage. If the circuit tests normal, replace the module that caused no communication.
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