Buick Regal: Interior Backlighting Malfunction

Diagnostic Instructions

• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Diagnostic Fault Information

1. Dimmer Switch Malfunction
2. Interior Backlighting Malfunction
3. Switch Indicator LED Backlighting Malfunction
4. Door Lock Indicator Malfunction

Circuit/System Description

The instrument panel dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The instrument panel dimmer switch provides a voltage signal to the body control module (BCM) that will increase as the brightness of the lights are increased and decrease as the brightness of the lights are decreased. The BCM provides a low reference, signal, and B+ voltage reference to the instrument panel dimmer switch. When the instrument panel dimmer switch is placed in the desired position, the dimmed voltage setting is applied from the instrument panel dimmer switch through the instrument panel dimmer switch signal circuit to the BCM. The BCM interprets the signal and applies a pulse width modulated voltage through the LED dimming 1 and dimming 2 control circuits illuminating the interior backlighting to the requested level of brightness.

The indicators/backlighting for the components listed below are controlled by the Switch Indicator LED Backlight Dimming Control Terminal 5 X1.

• A98 Front Overhead Console Assembly
• S13D Door Lock Switch - Driver (red LED indicator)
• S13P Door Lock Switch - Driver (red LED indicator)
• S48E Multifunction Switch - Center Console

Reference Information

Schematic Reference

Interior Lights Dimming Wiring Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Interior Lighting Systems Description and Operation

Electrical Information Reference

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information.

Circuit/System Verification

1. Ignition ON.

2. Verify the scan tool LED Backlight Dimming Command parameter changes between a high percentage to a low percentage while operating the dimmer switch from high to low.

• If the parameter does not change

Refer to Circuit/System Testing - Dimmer Switch Malfunction.

• Go to next step: If the parameter changes

3. Verify the switch indictor LED's for the components listed below turn ON and OFF while turning the switches ON and OFF.

• A98 Front Overhead Console Assembly
• S13D Door Lock Switch - Driver (red LED indicator)
• S13P Door Lock Switch - Driver (red LED indicator)
• S48E Multifunction Switch - Center Console
• If any of the switch indicator LED's do not turn ON and OFF

Refer to Circuit/System Testing - Switch Indicator LED Backlighting Malfunction.

• Go to next step: If all switch indicator LED's turn ON and OFF

4. Verify all backlighting components turn ON and OFF while commanding the LED Backlight Dimming ON and OFF with a scan tool.

• If all backlighting components do not turn ON and OFF

Refer to Circuit/System Testing - Interior Backlighting Malfunction.

• Go to next step: If all backlighting components turn ON and OFF

5. All OK.

Circuit/System Testing

Dimmer Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the S30 Headlamp Switch, ignition ON.

2. Test for B+ between the B+ reference circuit terminal 12 and ground.

• If less than B+

1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module.
2. Test for infinite resistance between the B+ reference circuit terminal 12 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 B+ reference 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 B+

3. Verify a test lamp does not illuminate between B+ and the signal circuit terminal 11.

• If the test lamp illuminates

1. Ignition OFF, disconnect the X2 harness connector at the K9 Body Control Module.
2. Test for infinite resistance between the signal circuit terminal 11 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 the test lamp does not illuminate

4. Test for B+ between the B+ reference circuit terminal 12 and the signal circuit terminal 11.

• If less than B+

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 11 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 B+

5. Test for B+ between the B+ reference circuit terminal 12 and the low reference circuit terminal 7.

• If less than B+

1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module, ignition ON.
2. Test for less than 1 V between the low reference circuit terminal 7 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 low reference 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 B+

6. Verify a test lamp does not illuminate between the B+ reference circuit terminal 12 and ground.

• If the test lamp illuminates

1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module, ignition ON.
2. Test for less than 1 V between the B+ reference circuit terminal 12 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 does not illuminate

7. Test or replace the S30 Headlamp Switch.

Interior Backlighting Malfunction

NOTE: Each component with backlighting may need to be disconnected to isolate a short to voltage or short to ground. Use the schematics to identify the following:

• Backlighting components the vehicle is equipped with
• Each component's control and ground circuit terminals
• Component locations on the backlighting control circuit

1. Ignition OFF, all doors closed, all accessories OFF, open and close drivers door, disconnect the harness connector at the component with inoperative backlighting. It may take up to 2 min for all vehicle systems to power down.

2. Test for less than 15 Ω between the appropriate ground circuit terminal 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. Connect a test lamp between the appropriate control circuit terminal and ground, ignition ON.

4. Verify the test lamp turns ON and OFF when commanding the LED Backlight Dimming ON and OFF with a scan tool.

• If the test lamp is always OFF

1. Ignition OFF, disconnect the appropriate harness connector listed below at the K9 Body Control Module.
   • X2 terminal 8
   • X7 terminal 9
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 appropriate harness connector listed below at the K9 Body Control Module, ignition ON.
   • X2 terminal 8
   • X7 terminal 9
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

5. Test or replace the component with inoperative backlighting.

Switch Indicator LED Backlighting Malfunction

NOTE: Each component with backlighting may need to be disconnected to isolate a short to voltage or short to ground. Use the schematics to identify the following:

• Backlighting components the vehicle is equipped with
• Each component's control and ground circuit terminals
• Component locations on the backlighting control circuit

1. Ignition OFF, all doors closed, all accessories OFF, open and close drivers door, disconnect the harness connector listed below. It may take up to 2 min for all vehicle systems to power down.

• S13D Door Lock Switch - Driver
• S13P Door Lock Switch - Driver

2. Test for less than 15 Ω between the ground circuit terminal 6 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 OFF, disconnect the harness connector at the appropriate component listed below, ignition ON.

• A98 Front Overhead Console Assembly
• S48E Multifunction Switch - Center Console

4. Place the interior backlighting dimmer switch in the HIGH position for high backlighting intensity.

5. Verify a test lamp illuminates between the appropriate control circuit terminal listed below and ground.

• A98 Front Overhead Console Assembly terminal 18
• S13D Door Lock Switch - Driver terminal 5
• S13P Door Lock Switch - Driver terminal 5
• S48E Multifunction Switch - Center Console terminal 3
• If the test lamp does not illuminate

1. Ignition OFF, disconnect the X1 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.

• Go to next step: If the test lamp illuminates

6. Place the interior backlighting dimmer switch in the LOW position for low backlighting intensity.

7. Verify a test lamp does not illuminate at FULL intensity between the appropriate control circuit listed below and ground.

• A98 Front Overhead Console Assembly terminal 18
• S13D Door Lock Switch - Driver terminal 5
• S13P Door Lock Switch - Driver terminal 5
• S48E Multifunction Switch - Center Console terminal 3
• If the test lamp illuminates at full intensity

1. Ignition OFF, disconnect the X1 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 does not illuminate at full intensity

8. Test or replace the component with the inoperative indicator.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Headlamp Switch Replacement
• Front Side Door Window Switch Replacement
• Rear Side Door Window Switch Replacement
• Door Lock Switch Replacement - Driver Side
• Parking Brake Actuator Switch Replacement
• Radio Control Switch Replacement - Steering Wheel
• Cruise Control Switch Replacement
• Ignition and Start Switch Replacement
• Head Up Display Switch Replacement
• Roof Console Replacement
• Control Module References for BCM replacement, programming, and setup

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