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Home >> Cadillac >> 2007 >> STS Base, 4.6 A, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 12 (Lighting Systems) >> Diagnostic Information and Procedures >> DTC B3420 >> Circuit/System Testing
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Circuit/System Testing

WARNING: This page is about a different car, the 2008 Cadillac SRX. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the harness connector at the rear headlamp leveling sensor.
  2. Ignition OFF, test for less than 5.0 ohms of resistance between the ground circuit terminal C and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, test for B+ between the voltage reference circuit terminal A and ground.
    • If less than the specified range, test the voltage reference circuit for a short to ground or an open/high resistance.
  4. Disconnect the X 112 harness connector at the right headlamp assembly.
  5. Ignition ON, verify that a test lamp does not illuminate between the rear headlamp leveling switch signal circuit terminal B and ground.
    • If the test lamp illuminates, test the signal circuit for a short to voltage. If the circuit tests normal, test or replace the left headlamp assembly.
  6. Disconnect the X 111 harness connector at the left headlamp assembly.
  7. Ignition OFF, verify that a test lamp does not illuminate between the rear headlamp leveling switch signal circuit terminal B and B+.
    • If the test lamp illuminates, test the signal circuit terminal B for a short to ground.
  8. Ignition OFF, verify that a test lamp does not illuminate between the rear headlamp leveling switch signal circuit terminal E and B+.
    • If the test lamp illuminates, test the signal circuit terminal E for a short to ground.
  9. Disconnect the harness connector at the front headlamp leveling sensor.
  10. Ignition OFF, verify that a test lamp does not illuminate between the front headlamp leveling switch signal circuit terminal 4 and B+.
    • If the test lamp illuminates, test the signal circuit terminal 4 for a short to ground.
  11. Connect the X 111 harness connector at the left headlamp assembly.
  12. Verify with a DMM that continuity is present between the rear headlamp leveling switch signal circuit terminal B and terminal E at the X 112 harness connector at the right headlamp assembly.
    • If continuity is not present, test the signal circuit for an open/high resistance. If the circuit tests normal, test or replace the left headlamp assembly.
  13. If all circuits test normal, test or replace the rear headlamp leveling sensor.
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