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Home >> Buick >> 2011 >> LaCrosse CXS >> Repair and Diagnosis >> External Pages >> Different car >> Section 169 (Keyless Entry System And Remote Functions) >> Diagnostic Information and Procedures >> DTC B3121 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2010 Buick LaCrosse. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: Verify that the pins are correct for all of the antennas. Make sure to fix any problems with the interior antennas first, before proceeding to the following diagnostics below regarding the exterior antennas. If any of the interior antenna DTCS B3122, B3123, B3124 is set, the diagnostic procedures on the exterior antennas will not work.
  1. Ignition OFF, disconnect the harness connector at the T10G rear fascia antenna.
  2. Ignition ON, verify a test lamp does not illuminate between the signal circuit terminal 1, connector on vehicle side, and vehicle ground and also does not illuminate between low reference signal circuit terminal 2, connector on vehicle side, and vehicle ground.
    • If the test lamp illuminates, disconnect the connector at the keyless entry control module, test the appropriate signal circuit for a short to voltage. If the circuit tests normal, replace the keyless entry control module.
  3. Connect a DMM, set to capture DC voltage using the MIN MAX function, between the signal circuit terminal 1 and vehicle ground.
    4. NOTE: Use DC voltage because comparing to vehicle ground.
  4. Activate the rear fascia antenna by manually pressing the rear closure touch pad. After hitting the min/max button looking for any voltage, verify the DMM captured a DC voltage signal.
    • If the DC voltage was not captured, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the keyless entry control module.
  5. Connect a DMM, set to capture DC voltage using the MIN MAX function, between the low reference circuit terminal 2 and vehicle ground.
  6. Activate the rear fascia antenna by manually pressing the rear closure touch pad. After hitting the min/max button looking for any voltage, verify the DMM captured a DC voltage signal.
    • If the DC voltage was not captured, test the low reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the keyless entry control module.
    • Clear DTCs then press the rear closure touch pad and check for DTCs again.
    • If DTC B3121 returns replace the T10G rear fascia antenna. Clear DTCs again then press the rear closure touch pad and check for DTCs.
    • If DTC B3121 returns, replace the keyless entry control module.
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