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Home >> Buick >> 2018 >> Regal GS >> Repair and Diagnosis >> Accessories & Equipment >> Interior/Illumination Lights >> Lighting System - Diagnostic Information And Procedures (B388B-P0504) And Symptoms >> Diagnostic Information and Procedures >> Courtesy Lamps Malfunction >> Circuit/System Testing

Circuit/System Testing

    NOTE:

    Each lighting component may need to be disconnected to isolate a short to ground. Use the schematics to identify the following:

    • Lighting components the vehicle is equipped with
    • Each component's control and ground circuit terminals
    • Component locations on the lighting control circuit
  1. Ignition OFF, disconnect the harness connectors at the appropriate components listed below, ignition ON.
    • A98 Front Overhead Console Assembly
    • E37R Dome/Reading Lamps - Rear (without C3U)
  2. Verify a test lamp illuminates between the B+ circuit terminal 1 and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Ignition OFF, remove the F41DA fuse at the X51A Fuse Block - Instrument Panel.
    2. Test for less than 2 Ω in the B+ circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Ignition OFF, remove the F41DA fuse at the X51A Fuse Block - Instrument Panel.
    2. Test for infinite resistance between the B+ circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the appropriate component listed below.
    • A98 Front Overhead Console Assembly
    • E37R Dome/Reading Lamps - Rear (without C3U)
    • Go to next step: If the test lamp illuminates 
  3. Ignition OFF, connect the harness connectors at the appropriate components listed below.
    • A98 Front Overhead Console Assembly
    • E37R Dome/Reading Lamps - Rear (without C3U)
  4. Ignition OFF, all doors closed, all accessories OFF, open and close drivers door, disconnect the harness connector at the appropriate component listed below. It may take up to 2 min for all vehicle systems to power down.
    • A3L Sunshade - Left
    • A3R Sunshade - Right
    • A98 Front Overhead Console Assembly
    • B163B Trailer Connector Detection Switch 2 (with VK0)
    • E27 Instrument Panel Compartment Lamp
    • E37J Dome/Reading Lamps - Left Roof Rail
    • E37H Dome/Reading Lamps - Right Roof Rail
    • E37R Dome/Reading Lamps - Rear
  5. Test for less than 15 Ω between the appropriate ground circuit terminal listed below and ground.
    • A3L Sunshade - Left terminal B
    • A3R Sunshade - Right terminal B
    • A98 Front Overhead Console Assembly terminal 5
    • B163B Trailer Connector Detection Switch 2 terminal A (with VK0)
    • E27 Instrument Panel Compartment Lamp terminal 2
    • E37J Dome/Reading Lamps - Left Roof Rail terminal 3
    • E37H Dome/Reading Lamps - Right Roof Rail terminal 3
    • E37R Dome/Reading Lamps - Rear terminal 3
    • If 15 Ω or greater 
    1. Ignition OFF.
    2. Test for less than 2 Ω in the ground circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, repair the open/high resistance in the ground connection.
    • Go to next step: If less than 15 Ω 
  6. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON.
    • A3L Sunshade - Left terminal A
    • A3R Sunshade - Right terminal A
    • A98 Front Overhead Console Assembly terminal 7
    • B163B Trailer Connector Detection Switch 2 terminal B (with VK0)
    • E27 Instrument Panel Compartment Lamp terminal 1
    • E37J Dome/Reading Lamps - Left Roof Rail terminal 1
    • E37H Dome/Reading Lamps - Right Roof Rail terminal 1
    • E37R Dome/Reading Lamps - Rear terminal 4
  7. Verify the test lamp turns ON and OFF when commanding the Inadvertent Load ON and OFF with a scan tool.
    • If the test lamp is always OFF 
    1. Ignition OFF, disconnect the X7 harness connector at the K9 Body Control Module.
    2. Test for infinite resistance between the control circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    3. Test for less than 2 Ω in the control circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K9 Body Control Module.
    • If the test lamp is always ON 
    1. Ignition OFF, disconnect the X7 harness connector at the K9 Body Control Module, ignition ON.
    2. Test for less than 1 V between the control circuit terminal and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the K9 Body Control Module.
    • Go to next step: If the test lamp turns ON and OFF 
  8. Test or replace the courtesy lamp.
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