GM Service Manual Online
For 1990-2009 cars only

The Scan Tool Data Definitions contains a brief description of all Lighting System related parameters available on the scan tool.

Body Control Module (BCM) Exterior Lighting

Ambient Light Sensor: The scan tool displays the output voltage of the ambient light sensor based on the intensity of light detected. As the light intensity increases, the displayed voltage decreases. In the Day state, a low voltage not less than approximately 0.67 volt is displayed and the daytime running lamps (DRL) will be active. In the Night state, a voltage up to approximately 4.52 volts is displayed and the headlamps will be active.

Ambient Light Status: The scan tool displays the state of the ambient light sensor based on the intensity of light detected. In the Day state, the daytime running lamps (DRL) will be active. In the Night state, the headlamps will be active.

Auto Hdlp. Disable Sw.: The scan tool displays the state of the momentary auto headlamp defeat position of the headlamp switch. The scan tool will display Active when the auto headlamp defeat switch position is momentarily selected.

Backup Lamps: The scan tool displays On when backup lamp operation is requested.

DRL Relay Command: The scan tool displays On when DRL mode is requested and the daytime running lamp (DRL) relay is activated.

Flash to Pass Switch: The scan tool displays Inactive/Active. When the multifunction switch is placed on the FTP position, the scan tool will display Active.

Front Fog Lamp Relay Command: The scan tool displays ON/OFF. When the fog lamp switch is placed in the ON position and fog lamp relay activation is requested, the scan tool will display ON.

Front Fog Lamp Switch: The scan tool displays Inactive/Active. When the front fog lamp switch is placed in the ON position, the scan tool will display Active.

Hazard Lamp Switch:  The scan tool displays Inactive/Active. When the hazard switch is placed in the ON position, the scan tool will display Active.

Headlamp Switch: The scan tool displays Inactive/Active. When the headlamp switch is placed in the OFF position, the scan tool will display Inactive.

High Beam Relay Command: The scan tool displays the commanded state of the high beam relay. When the headlamp dimmer switch is placed in the HIGH position and the relay is activated, the scan tool will display ON.

High Beam Select Switch: The scan tool displays Inactive/Active. When the headlamp dimmer switch is placed in the HIGH position, the scan tool will display Active.

Left Turn Signal Switch: The scan tool displays Inactive/Active. When the turn signal switch is placed in the LEFT turn position, the scan tool will display Active.

LF Turn Signal: The scan tool displays the commanded state of the left front turn signal. When the turn signal switch is placed in the LEFT turn position, the scan tool display will display On when the lamp is illuminated and Off during the off portion of the cycle.

LR Turn Signal: The scan tool displays the commanded state of the left rear turn signal. When the turn signal switch is placed in the LEFT turn position, the scan tool display will display On when the lamp is illuminated and Off during the off portion of the cycle.

Low Beam Relay Command: The scan tool displays the commanded state of the high beam relay. When the headlamp dimmer switch is placed in the LOW position and the relay is inactive, the scan tool will display ON.

Park Lamp Relay Cmd.: The scan tool displays the commanded state of the park lamp relay. When the headlamp switch is placed in the PARK position and the relay is activated, the scan tool will display ON.

Park Lamp Switch: The scan tool displays Inactive/Active. When the headlamp switch is in the PARK position, the scan tool will display Active.

Right Turn Signal Switch: The scan tool displays Inactive/Active. When the turn signal switch is placed in the RIGHT turn position, the scan tool will display Active.

RF Turn Signal: The scan tool displays the commanded state of the right front turn signal. When the turn signal switch is placed in the RIGHT turn position, the scan tool display will display On when the lamp is illuminated and Off during the off portion of the cycle.

RR Turn Signal: The scan tool displays the commanded state of the right rear turn signal. When the turn signal switch is placed in the RIGHT turn position, the scan tool display will display On when the lamp is illuminated and Off during the off portion of the cycle.

Stop Lamp Sw. Status: The scan tool displays the state of the stop lamp switch. When the brake pedal is at rest and the stop lamp switch contacts are closed, the scan tool will display approximately 1023 counts. When the brake pedal is pressed and the stop lamp switch contacts are open, the scan tool will display 1 count.

Stop Lamp Relay Command: The scan tool displays the commanded state of the stop lamp relay. When the brake is applied and the relay is activated, the scan tool will display ON.

Body Control Module (BCM) Inputs

Park Brake Switch: The scan tool display Released/Applied. When the park brake is set, the scan tool will display Applied.

Body Control Module (BCM) Interior Lighting

Courtesy Lamp PWM Cmd.: The scan tool displays the commanded duty cycle state of the courtesy lamps. When the courtesy lamps are activated the scan tool will display 100%.

Cruise Ctrl. LED Dimming Cmd.: The scan tool displays the commanded duty cycle state of the cruise control switch LED indicator . The scan tool will display the percentage of illumination level based on the instrument panel (I/P) dimmer switch position.

Ctsy. Lamp Actv. Reason: The scan tool displays the condition of why the courtesy lamps have been activated. When the courtesy lamps are activated, the scan tool will display either Off, Panic, Manual, Air Bag, Door Open, RFA, RFA Theft, Door Closed, Exit, or Manual Defeat depending on which function requested courtesy lamp illumination.

Dimming Control Reference: The scan tool displays the reference voltage of the instrument panel (I/P) dimmer switch. When the instrument panel (I/P) dimmer switch is in the full dim position the scan tool will display approximately 3 volts. When the I/P dimmer switch is in the full bright position the scan tool will display approximately 3 volts.

Dimming Control Signal: The scan tool displays the percentage of the voltage signal output of the instrument panel (I/P) dimmer switch. When the I/P dimmer switch is in the full dim position the scan tool will display 8%. When the I/P dimmer switch is in the full bright position the scan tool will display 100%.

Dimming Control Signal: The scan tool displays the voltage output of the instrument panel (I/P) dimmer switch. When the I/P dimmer switch is in the full dim position the scan tool will display approximately 0.23 volt . When the I/P dimmer switch is in the full bright position the scan tool will display approximately 3 volts.

Incandescent Dimming PWM Cmd.: The scan tool displays the pulse width modulation (PWM) percentage of the incandescent backlighting voltage signal output of the instrument panel (I/P) dimmer switch. When the I/P dimmer switch is in the full dim position the scan tool will display approximately 28%. When the I/P dimmer switch is in the full bright position the scan tool will display 100%.

LED Dimming PWM Cmd.: The scan tool displays the pulse width modulation (PWM) percentage of the LED backlighting voltage signal output of the instrument panel (I/P) dimmer switch. When the I/P dimmer switch is in the full dim position the scan tool will display approximately 5%. When the I/P dimmer switch is in the full bright position the scan tool will display 100%.

Body Control Module (BCM) Outputs

Brake Applied Output Signal: The scan tool displays ON/OFF. When the brake switch is applied, the scan tool will display ON.

Driver Door Switch Inputs

Driver Door Open Sw.: The scan tool displays Inactive/Active. When the driver door is open, the scan tool will display Active.

Driver Door Switch Outputs

Memory Switch Backlight: The scan tool displays the percentage of the memory seat switch backlighting level based on the instrument panel (I/P) dimmer switch position. When the I/P dimmer switch is in the full dim position the scan tool will display approximately 5%. When the I/P dimmer switch is in the full bright position the scan tool will display approximately 60%.

Window Switch Backlight: The scan tool displays the percentage of the window switch backlighting level based on the instrument panel (I/P) dimmer switch position. When the I/P dimmer switch is in the full dim position the scan tool will display approximately 5%. When the I/P dimmer switch is in the full bright position the scan tool will display approximately 60%.

Export Body Control Module (XBCM) Data Display

Battery Voltage: The scan tool displays the battery voltage input to the XBCM.

Rear Fog Lamp Relay Command: The scan tool displays ON/OFF. When the rear fog lamp switch is placed in the ON position and rear fog lamp relay activation is requested, the scan tool will display ON.

Rear Fog Lamp Switch: The scan tool displays Inactive/Active. When the rear fog lamp switch is placed in the ON position, the scan tool will display Active.

Trailer Left Bulb Out Signal: The scan tool displays counts. When the XBCM detects that a trailer is connected and that a left trailer bulb is inoperative, the scan tool will display 0 counts. When the XBCM detects that a trailer is connected and that a left trailer bulb is operative, the scan tool will display 255 counts.

Trailer Right Bulb Out Signal: The scan tool displays counts. When the XBCM detects that a trailer is connected and that a right trailer bulb is inoperative, the scan tool will display 0 counts. When the XBCM detects that a trailer is connected and that a right trailer bulb is operative, the scan tool will display 255 counts.

Trailer Detection Input: The scan tool displays ON/OFF. When a trailer is connected to the vehicle and a voltage signal is received through the trailer harness to the XBCM, the scan tool will display ON.

Trailer Fog Lamp Relay Command: The scan tool displays ON/OFF. When the rear fog lamp switch is placed in the ON position and trailer rear fog lamp relay activation is requested, the scan tool will display ON.

Passenger Door Switch Inputs

Passenger Door Open Sw.: The scan tool displays Inactive/Active. When the passenger door is open, the scan tool will display Active.

Passenger Door Switch Outputs

Memory Switch Backlight: The scan tool displays the percentage of the memory seat switch backlighting level based on the instrument panel (I/P) dimmer switch position. When the I/P dimmer switch is in the full dim position the scan tool will display approximately 5%. When the I/P dimmer switch is in the full bright position the scan tool will display approximately 60%.

Window Switch Backlight: The scan tool displays the percentage of the window switch backlighting level based on the I/P dimmer switch position. When the I/P dimmer switch is in the full dim position the scan tool will display approximately 5%. When the I/P dimmer switch is in the full bright position the scan tool will display approximately 60%.