For 1990-2009 cars

## Exterior Lighting Systems Description and Operation LWB

The exterior lighting system consists of the following lamps:

• | The headlamps

• | The front fog lamps

• | The rear fog lamp (export only)

• | The park, tail and marker lamps

• | The exterior courtesy lamps

• | The turn signal/hazard lamps

• | The side repeater lamps (export only)

• | The stop lamps

• | The backup lamps

• | The cargo lamps

• | The clearance lamps

#### Headlamps

The headlamps may be turned ON in 2 different ways. First, when the driver places the headlamp switch in the HEADLAMP position, for normal operation. Second, with the headlamp switch placed in the AUTO position, for automatic lamp control (ALC).

Headlamp ON/OFF control is determined by the body control module (BCM) by a signal on the headlamp switch on input circuit when the headlamp switch is in the HEAD position. When the headlamp switch is in the AUTO position, the BCM determines headlamps ON/OFF by the voltage from the ambient light sensor.

If the headlight switch is left in the ON position, the inadvertent power control feature will turn OFF the headlights approximately 10 seconds after the ignition switch is turned to the OFF position. If the driver places the headlight switch in the ON position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the headlights will remain ON until turned OFF or the battery runs flat.

The high beam indicator is illuminated when the instrument cluster receives a GMLAN serial data message from the BCM that the high beams are illuminated.

#### High Beams

The high beam headlamps receive voltage from the headlamp high relay located in the underhood fuse block. The BCM controls the relay on the headlamp high beam relay control circuit. High beam control is determined by a signal on the headlamp dimmer switch high beam signal circuit from the turn signal multifunction switch. When the headlamp dimmer switch signal circuit is grounded, the BCM grounds the headlamp high beam relay control circuit, illuminating the high beam headlamps. The right and left high beam circuits are independent and are fused independently in the underhood fuse block.

#### Low Beams - Standard

The low beam headlamps receive voltage from the headlamp low beam relay located in the underhood fuse block. The BCM controls the relay on the headlamp low beam relay control circuit. Low beam control is activated when the headlamp switch is placed in the headlamp ON position grounding the headlamp switch headlamps on signal circuit to the BCM. The right and left low beam circuits are independent are fused independently in the underhood fuse block.

#### Fog Lamps

With both the ignition switch in the RUN position, and the park lamps ON, the fog lights will illuminate when the driver depresses the fog lamp switch. The BCM receives the park lamp ON signal from the interior park lamps supply voltage signal circuit. With the headlamp switch in either the park or headlamp position, and the fog lamp switch is in the ON position, the BCM will ground the fog lamp relay control circuit causing the relay to energise. The current flows from the fog lamp relay to both front fog lamps. The state of the fog lamps will remain the same until the fog lamp switch position is changed, or the ignition switch is cycled OFF and ON. Fog lamp operation will be cancelled whenever the park lamps are turned OFF or the high beam headlights have been selected.

#### Park, Tail and Marker Lamps

The park, tail and marker lamps, including the license lamps, are turned ON when the headlamp switch is placed in the PARK or HEAD position or anytime the headlights are requested. The underhood fuse block supplies battery positive voltage to both the park lamp relay switch contacts and the park lamp coil circuit. The BCM provides a ground or control circuit to the park lamp relay coil circuit. When the park lamps are turned ON, the BCM energises the park lamp relay. If the headlight switch is left in the ON position, the inadvertent power control feature will turn OFF the park, tail and marker lamps approximately 10 seconds after the ignition switch is turned to the OFF position. If the driver places the headlight switch in the ON position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the park, tail and marker lamps will remain ON until turned OFF or the battery runs flat.

#### Exterior Courtesy Lamps

The BCM, driver door switch, and the passenger door switch communicate through the GMLAN serial data system. The driver door switch and passenger door switch supply power and ground to the left and right exterior lamps respectively. When the BCM commands illuminated entry, a command is also sent to the door switches for illumination of the exterior courtesy lamps. If the door locks are activated to the LOCK position, or if the ignition switch is turned to either the ON or RUN position the exterior courtesy lamps will deactivate immediately.

#### Turn Signal/Hazard Lamps

When the turn signal multifunction switch is placed in either the left or right position, a ground signal is completed from the turn signal switch to the BCM. The BCM then sends an ON-OFF voltage signal through the fuses to the appropriate turn signal and side repeater lamps or to all of the turn signal fuses for hazard operation. An audio chime is also activated when the turn signals are ON. The instrument panel cluster (IPC) receives the signals to activate the turn signal indicators over the GMLAN serial data system. The hazard warning switch is an integral part of the infotainment fascia, when the hazard warning switch is pressed, the infotainment unit communicates with the BCM via the GMLAN serial data system to activate the hazard warning lamps, the hazard warning switch is NOT connected directly to the turn signal/hazard lamp circuit. When activated all turn signal lamps will flash including both IPC turn indicators.

#### Stop Lamps

When the driver presses the brake pedal, the a variable voltage signal from the brake pedal position sensor (BPPS) is supplied to the BCM. The BCM then supplies voltage to stop lamp supply voltage circuit applying power to the stop lamps and center high mount stop lamp (CHMSL). The BCM also supplies voltage to the transmission control module (TCM), and powertrain control module (ECM) through a dedicated circuit.

#### Backup Lamps

The backup lamp request signal is sent from the ECM to the BCM on the GMLAN serial data system. This signal is based on the park neutral position (PNP) switch signal. The BCM supplies voltage to the backup relay and to the automatic day/night mirror when the vehicle is in reverse. The backup relay supplies a voltage on the backup lamp supply voltage circuit to the backup lamps.

#### Cargo Lamps

The cargo lamp is controlled by the dome lamp control circuit. There is not a separate switch to turn the cargo lamps ON and OFF.

#### Clearance Lamps

The clearance lamps, are turned ON when the headlamp switch is placed in the PARK or HEAD position or anytime the headlamps are requested. The underhood fuse block supplies battery positive voltage to both the park lamp relay switch contacts and the park lamp coil circuit. The BCM provides a ground or control circuit to the park lamps relay coil circuit. When the park lamps are turned ON, the BCM energises the park lamp relay. If the headlamp switch is left in the ON position, the inadvertent power control feature will turn OFF the park, tail and clearance lamps approximately 10 minutes after the ignition switch is turned to the OFF position. If the driver places the headlamp switch in the ON position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the park, tail and marker lamps will remain ON until turned OFF or the battery runs dead.

#### Low Beams - High Intensity Discharge (HID)

Normal operation of the HID system starts at the ballast. The headlamp ballast input connector receives battery positive voltage from fuses in the underhood fuse block. When the low beam headlamps are requested the low beam relay supplies voltage to the ballast on the right headlamp low beam supply voltage circuit and the left headlamp low beam supply voltage circuit, which in turn begins the low beam operation as follows. As soon as the input power is applied, the ballast draws 20 amps from the battery for 5-10 seconds, depending on the input voltage level. The ballast is then able to charge the 2 outputs leading to the start to -360 volts and +800 volts. Negative 360 volts and +800 volts are the voltages needed by the starter to strike or start the lamp. HID headlamps do not have filaments like traditional bulbs, instead, the starter uses a high voltage transformer to convert the +800 volts input power into 25,000 volts. The increased voltage is used in order to create an arc between the electrodes in the bulb. The creation of this arc begins the start up process.

#### Low Voltage Operation of HID Headlamps

The BCM monitors the vehicle system voltage while in the RUN power mode. When the system voltage drops below 8.9 volts, the following will occur:

• | STAGE 1: If the low beam headlamps are ON, either manually or automatically, the BCM will turn ON the high beam headlamps by activating the High Beam output.

• | STAGE 2: When the system voltage drops below 8.5 volts, the following will occur:

- | If the low beam headlamps are currently ON, either manually or automatically, the BCM will turn OFF the low beam headlamps by deactivating the Low Beam output.

- | If the headlamps are then turned ON manually, the manual switch redundancy will cause the low beam headlamps to remain ON.

If during the same ignition cycle, the BCM enters either STAGE 1 or STAGE 2 operations noted above, and then determines that the system voltage has risen, the following will occur:

• | If the BCM has entered STAGE 2 operation, it will not return to STAGE 1 operation until the system voltage rises above 9.4 volts.

• | If the BCM has entered STAGE 1 operation, it will not return to normal operation until the system voltage rises above 9.8 volts.

#### Electrical System Requirements with HID

Ensure that the battery and the harness are capable of supplying up to 20 amps of current per ballast, with less than 2 volts of system loss or voltage drop. Each ballast requires the 20 amps in order to ensure normal startup and run up of the lamp. Run up is the term used to describe the extra power level given to the bulb from the -360-volt ballast output. The input current during the steady state operation is 3.4 amps at 12.8 volts.

#### Run Up of the HID Lamp

After the lamp receives the strike from the starter and the arc is established, the ballast uses its -360-volt output in order to provide the run up power needed in order to keep the lamp ON. The lamp rapidly increases in intensity from a dim glow to a very high-intensity, bright light called a steady state. Within 2 seconds of the arc being established in the bulb, 70 percent of steady state is complete. 100 percent of the steady state is completed within 30 seconds. A 75-watt power level is necessary in order to bring the lamp to a steady state in the required period of time.

#### When to Change the HID Bulb

Bulb failure occurs when the bulb gets older and becomes unstable. The bulb may begin shutting itself OFF sporadically and unpredictably at first, perhaps only once during a 24 hour period. When the bulb begins shutting itself OFF occasionally, the ballast will automatically turn the bulb back ON again within 0.5 second. The ballast will re-strike the bulb so quickly that the bulb may not appear to have shut OFF. As the bulb ages, the bulb may begin to shut OFF more frequently, eventually over 30 times per minute. When the bulb begins to shut OFF more frequently, the ballast receives excessive, repetitive current input (20 amps). Repetitive and excessive restarts or re-strikes, without time for the ballast to cool down, will permanently damage the ballast. As a safeguard, when repetitive re-strikes are detected, the ballast will not attempt to re-strike the lamp. The ballast then shuts down and the bulb goes out.

The following symptoms are the noticeable signs of bulb failure:

• | Flickering light caused in the early stages of bulb failure

• | Lights go out caused when the ballast detects excessive, repetitive bulb re-strike

• | Color change--The lamp may change to a dim pink glow.

Input power to the ballast must be terminated in order to reset the ballasts fault circuitry. In order to terminate the input power to the ballast, turn the lights OFF and back ON again. Turning the lights OFF and back ON again resets all of the fault circuitry within the ballast until the next occurrence of excessive, repetitive bulb re-strikes. When excessive, repetitive bulb re-strikes occur, replace the starter/arc tube assembly. The ballast will begin the start-up process when the starter/arc tube assembly is replaced. Repeatedly resetting the input power can overheat the internal components and cause permanent damage to the ballast. Allow a few minutes of cool-down time in between reset attempts.

Bulb failures are often sporadic at first, and difficult to repeat. Technicians can identify bulb failure by observing if the problem gets progressively worse over the next 100 hours of operation.

#### Light Color (w/HID)

HID headlamps have a different color rating than regular headlamps. The range of white light that is acceptable is broad when compared to halogens. Therefore, some variation in headlight coloring between the right and left headlamp will be normal. One HID at the end of the normal range may appear considerably different in color from one at the other end of the range. A difference in color is normal. Replace the arc tube only if the arc tube is determined to be at the bulb failure stage.

#### Automatic Headlamp Levelling

The Automatic Headlamp Levelling systems consist of the following components:

• | Headlamp levelling module

• | Headlamp levelling actuator - left

• | Headlamp levelling actuator - right

• | Front suspension position sensor

• | Rear suspension position sensor

The automatic headlamp levelling system automatically maintains the vertical alignment of the headlamps when the vehicle load and driving conditions change. The suspension position sensors send an output to the headlamp levelling module as the vehicle suspension compresses and rebounds. The headlamp levelling module determines vehicle pitch based on outputs from the front and rear suspension position sensors. The headlamp levelling module calculates the difference in vehicle pitch and sends a command to the headlamp levelling actuators. The headlamp levelling actuators drive the headlamps to the position commanded by the headlamp levelling module. The headlamp levelling system also monitors the performance of the high intensity discharge (HID) bulb and ballast. When the headlamp switch is placed in the ON position the headlamps will go down, and then back up to the centre position.