Circuit/System Testing

NOTE: If more than one control module is not communicating use Data Communication Schematics to determine which control module is closest to the DLC. Start diagnostics with that control module.
Terminal and connector identifiers will be different depending on the individual control module being tested. Use Schematic Reference and Connector End View Reference to determine which connector and terminal to access.

Using the DTC Descriptor and Diagnostic Aids, determine the control module that is not communicating that should be tested.
Ignition OFF, disconnect the harness connector at the control module that is not communicating.
Ignition OFF, test for less than 2 ohms between each ground circuit terminal and ground.
- If greater than specified range, test the ground circuit for an open/high resistance.

NOTE: Only the high speed GMLAN modules have a wired serial data wake up circuit. Refer to the module schematics to identify which control modules have a wake up circuit. If the control module that is not communicating does not have a serial data wake up circuit, proceed to step 5.

Ignition ON, verify that a test lamp illuminates between the high speed GMLAN serial data wake up circuit OR the accessory wake up serial data circuit terminal and ground.
- If the test lamp does not illuminate, test the wake up circuit for an open/high resistance. If the circuits test normal, replace the K9 body control module (BCM).
Ignition ON, verify that a test lamp illuminates between each B+ circuit terminal and ground.
- If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the control module for a short to ground. If the circuits test normal, replace the appropriate control module.
Ignition ON, verify that a test lamp illuminates between each ignition voltage circuit terminal and ground.
- If the test lamp does not illuminate, test the ignition voltage circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the control module for a short to ground. If the circuits test normal, replace the appropriate control module.
Ignition OFF for 60 seconds, test for less than 1 Ω in each GMLAN serial data circuit between the non-communicating control module and the control module that displays the DTC.
- If greater than specified range, test the GMLAN serial data circuit for open/high resistance.
If all circuits test normal, replace the control module that is not communicating.