GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2007 🢒 Lucerne 🢒 DTC 🢒 DTC B2625

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.

DTC Descriptor

DTC B2625 00: Display Dimming Pulse Width Modulation (PWM) Output Circuit

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

LED Dimming Supply

B2625 00

2

1

--

  1. Interior Backlighting Does Not Dim
  2. Interior Backlighting Inoperative

Circuit/System Description

The BCM supplies a voltage reference through the instrument panel (I/P) dimming voltage reference circuit to the interior lamp dimmer switch, which is part of the headlamp switch. When the dimmer switch is placed in a desired brightness position, reference voltage is applied through the dimmer switch rheostat and the I/P lamps dimmer switch signal circuit to the BCM. The BCM interprets this voltage signal then applies a pulse width modulated (PWM) voltage through the LED dimming supply circuit illuminating the HVAC control module to the requested level.

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

The BCM detects a short to ground on the LED dimming supply circuit.

Action Taken When the DTC Sets

The BCM will not attempt to illuminate the LED indicator lamps.

Conditions for Clearing the DTC
    • The condition responsible for setting the DTC no longer exists.
    • A history DTC will clear once 100 consecutive malfunction ignition cycles have occurred.

Reference Information

Schematic Reference

Interior Lights Dimming Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

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

Scan Tool Reference

    •  Scan Tool Output Controls
    •  Scan Tool Data List
    •  Scan Tool Data Definitions

Circuit/System Verification

Ignition ON, cover the ambient light sensor, vary the interior lamp dimming switch from dim to full bright. The LED lamps should dim and then become full bright.

Circuit/System Testing
  1. Ignition OFF, disconnect the harness connectors at all components fed by the LED backlight dimming supply circuit terminal 25 C3.
  2. Ignition ON, clear the DTC with a scan tool.
  3. Operate the vehicle within the conditions for running the DTC and verify the DTC does not reset.
    4. ⇒If the DTC resets, test the LED dimming supply circuit for a short to ground. If the circuit test normal, replace the BCM.
  4. Reconnect each component one at a time and verify that the DTC does not reset as current.
    5. ⇒If the DTC resets as current, test or replace the component responsible for setting the DTC.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for BCM and HVAC control module replacement, setup, and programming