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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 >> Dome Lamps Malfunction >> Circuit/System Testing

Circuit/System Testing

Dome Lamp Switch Malfunction

  1. Ignition OFF, all doors closed, all accessories OFF, open and close drivers door, disconnect the harness connector at the A98 Front Overhead Console Assembly. It may take up to 2 min for all vehicle systems to power down.
  2. Test for less than 15 Ω between the ground circuit terminal 5 and ground.
    • 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 
  3. Ignition ON.
  4. Verify the scan tool Interior/Courtesy Lighting Master Switch parameter is Door.
    • If Cancel 
    1. Ignition OFF, disconnect the X7 harness connector at the K9 Body Control Module.
    2. Test for infinite resistance between the signal circuit terminal 21 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 On 
    1. Ignition OFF, disconnect the X2 harness connector at the K9 Body Control Module.
    2. Test for infinite resistance between the signal circuit terminal 3 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K9 Body Control Module.
    • Go to next step: If Door 
  5. Install a 3 A fused jumper wire between the signal circuit terminal 21 and ground.
  6. Verify the scan tool Interior/Courtesy Lighting Master Switch parameter is Cancel.
    • If not Cancel 
    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 signal circuit terminal 21 and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for less than 2 Ω in the signal 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.
    • Go to next step: If Cancel 
  7. Install a 3 A fused jumper wire between the signal circuit terminal 3 and ground.
  8. Verify the scan tool Interior/Courtesy Lighting Master Switch parameter is On.
    • If not On 
    1. Ignition OFF, disconnect the X2 harness connector at the K9 Body Control Module, ignition ON.
    2. Test for less than 1 V between the signal circuit terminal 3 and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for less than 2 Ω in the signal 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.
    • Go to next step: If On 
  9. Test or replace the A98 Front Overhead Console Assembly.

Dome Lamps Malfunction

    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
    • B177 Rain/Ambient Light Sensor Module (with CE1)
    • E37R Dome/Reading Lamps - Rear (with C93)
  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
    • B177 Rain/Ambient Light Sensor Module (with CE1)
    • E37R Dome/Reading Lamps - Rear (with C93)
    • 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
    • B177 Rain/Ambient Light Sensor Module (with CE1)
    • E37R Dome/Reading Lamps - Rear (with C93)
  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.
    • A98 Front Overhead Console Assembly
    • E37H Dome/Reading Lamps - Left Roof Rail (with C3U)
    • E37J Dome/Reading Lamps - Right Roof Rail (with C3U)
    • E37R Dome/Reading Lamps - Rear (without C3U)
    • E1AA Floor Accent Lamp - Left Front (with C93)
    • E1AB Floor Accent Lamp - Right Front (with C93)
  5. Test for less than 15 Ω between the appropriate ground circuit terminal listed below and ground.
    • A98 Front Overhead Console Assembly terminal 5
    • E37H Dome/Reading Lamps - Left Roof Rail terminal 3 (with C3U)
    • E37J Dome/Reading Lamps - Right Roof Rail terminal 3 (with C3U)
    • E37R Dome/Reading Lamps - Rear terminal 3 (without C3U)
    • E1AA Floor Accent Lamp - Left Front terminal 2 (with C93)
    • E1AB Floor Accent Lamp - Right Front terminal 2 (with C93)
    • 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.
    • A98 Front Overhead Console Assembly terminal 8
    • E37H Dome/Reading Lamps - Left Roof Rail terminal 4 (with C3U)
    • E37J Dome/Reading Lamps - Right Roof Rail terminal 4 (with C3U)
    • E37R Dome/Reading Lamps - Rear terminal 2 (without C3U)
    • E1AA Floor Accent Lamp - Left Front terminal 1 (with C93)
    • E1AB Floor Accent Lamp - Right Front terminal 1 (with C93)
  7. Verify the test lamp turns ON and OFF when commanding the Courtesy Lamps 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 appropriate courtesy/dome Lamp.
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