For 1990-2009 cars

### 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 Descriptors

DTC B2555 05: Passenger Compartment Lamp Control Circuit Short to Battery/Open.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Courtesy Lamp Control Circuit | 1 | B2555 05 | B2555 05 | --
Courtesy Lamps Supply Voltage Circuit | 2 | 2 | -- | --
Dome/Reading Lamp Ground Circuit | -- | 3 | 3 | --

1. Courtesy Lamps Always On
2. Courtesy Lamps Inoperative
3. Dome/Reading Lamp(s) Inoperative

### Circuit/System Description

The INT LIGHT fuse supplies battery voltage to the body control module (BCM). The BCM applies battery voltage to the dome lamp and inside rear view mirror through the courtesy lamp supply voltage circuit. The dome lamp is controlled by a 3 position (OFF, DOOR, ON) switch. When the dome lamp switch is placed in the DOOR position the lamps are controlled by the BCM. When any door is opened, the jam switch contacts close and the BCM recieves a door-open input. If the BCM recieves a door lock or unlock input the BCM will activate the courtesy lamp control circuit, providing ground to the dome/reading lamps.

### Conditions for Running the DTC

• | Battery voltage must be between 9-16 volts.

• | A message is sent from the BCM over the GM LAN serial data circuit to the driver door and passenger door switches to activate the door courtesy lamps.

### Conditions for Setting the DTC

• | DTC B2555 05 will set when the BCM detects a short to voltage in the courtesy lamp control circuit.

• | It takes 1.0 second for the code to set.

• | BCM is unable to change pulse width modulated (PWM) backlighting when park lamps are on.

• | Park lamps On and Day Night Mode status is equal to Night and Parade Mode status and is Correct or True.

• | Park lamps On and Parade Mode status is Incorrect or False.

### Action Taken When the DTC Sets

DTC B2555 05 is present, when a open or short to voltage on the courtesy lamp control circuit is present.

### Conditions for Clearing the DTC

• | The condition responsible for setting the DTC no longer exists.

• | A scan tool CLEAR DTCs command is issued for that switch module.

• | A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

### Reference Information

#### Schematic Reference

Interior Lights 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 Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### Circuit/System Testing

1. Disconnect the Dome Lamp assembly.
2. Connect a test lamp between the courtesy lamp control circuit terminal B of the Dome Lamp and ground.

⇒ | If the test lamp illuminates, locate and repair a short to voltage in the courtesy lamp control circuit.

⇒ | If the test lamp does not illuminate, locate and repair a short to ground in the courtesy lamp control circuit.

3. If circuits test OK, replace the BCM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for BCM replacement, setup, and programming.