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Home >> Buick >> 2015 >> Regal GS, AWD >> Repair and Diagnosis >> Accessories & Equipment >> Interior/Illumination Lights >> Lighting System - Diagnostic Information And Procedures >> Diagnostic Information and Procedures >> DTC B258A: Low Beam >> Circuit/System Testing

Circuit/System Testing

  1. Ignition OFF, disconnect the KR49 Headlamp Low Beam Relay.
  2. Connect a test lamp between the control circuit terminal 85 and B+, ignition ON.
  3. Verify the test lamp turns ON and OFF when commanding the Low Beams ON and OFF with a scan tool.
    • If the test lamp is always OFF 
    1. Ignition OFF, disconnect the X5 harness connector at the K9 body Control Module, ignition ON.
    2. Test for less than 1V between the control circuit terminal and ground.
      • If 1V or greater, repair the short to voltage on the circuit.
      • If less than 1V
    3. Ignition OFF.
    4. Test for less than 2Ω in the control circuit end to end.
      • If 2Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2Ω, replace the K9 body Control Module.
    • If the test lamp is always ON 
    1. Ignition OFF, disconnect the X5 harness connector at the K9 body Control Module.
    2. Test for infinite resistance between the control circuit terminal and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K9 body Control Module.
    • If the test lamp turns ON and OFF 
  4. Test or replace the KR49 Headlamp Low Beam Relay.
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