LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Cadillac >> 2011 >> STS AWD >> Repair and Diagnosis >> Engine Performance >> System >> Data Communications System >> Diagnostic Information and Procedures >> DTC U2105-U2199 >> Circuit/System Testing
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Circuit/System Testing

IMPORTANT:

If more than one control module is not communicating use Data Communication Schematics  to determine which control module is closest to the data link connector (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.

  1. Using the DTC Descriptor and Diagnostic Aids, determine the control module that is not communicating that should be tested.
  2. Ignition OFF, disconnect the harness connector of the control module that is not communicating.
  3. Test for less than 10 Ω between each ground circuit terminal and ground.
    • If greater than specified range, test the ground circuit for an open/high resistance.
  4. If equipped, 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 control circuits of the control module for a short to ground. If the circuits test normal, replace the appropriate control module.
  5. If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground.
    • If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the control circuits of the control module for a short to ground. If the circuits test normal, replace the appropriate control module.
    6. IMPORTANT:

    Only the high speed GMLAN modules have a serial data wake up circuit OR an accessory voltage circuit, and the BCM is the output for these circuits. Refer to the control module schematics to identify which control modules have these circuits. If the control module that is not communicating does not have any of these circuits, proceed to step 7.

  6. If equipped, ignition ON, verify that a test lamp illuminates between the serial data wake up circuit OR the accessory voltage circuit and ground.
    • If the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.
  7. Test for less than 2 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 an open/high resistance.
  8. If all circuits test normal, replace the control module that is not communicating.
scientia non olet · About LEMON Manuals