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Testing the Serial Data Circuit for an Open/High Resistance

  1. If equipped with a JX 405 splice pack, ignition ON, verify the scan tool communicates with one or more control modules connected to the JX 405 splice pack.
    • If all control modules on the JX 405 spice pack do not communicate, test the serial data circuit between the JX 205 and JX 405 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 205 if the control modules not communicating are connected to the JX 205 splice pack
    • JX 405 if the control modules not communicating are connected to the JX 405 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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