Headlamp: Description and Operation
HEADLAMPSThe headlamps may be turned on in three different ways:
- When the headlamp switch is placed in the ON position, for normal operation.
- When the headlamp switch is placed in the OFF position, and the twilight delay switch is moved out of the OFF position for automatic lamp control (ALC).
- When the headlamp switch is placed in the OFF position, the twilight delay switch is moved out of the OFF position, and the windshield wipers are ON in daylight conditions, after a six second delay.
During ALC the headlamps will be in day time running lamp (DRL) operation in daylight conditions, or low beam operation in low light conditions. When all exterior lighting controls are inactive and nighttime conditions are sensed, a HEADLAMPS SUGGESTED message will appear on the driver information center (DIC), after the IPC receives a class 2 message from the DIM. The message will also appear if the wiper activated headlamps feature is OFF due to the twilight sentinel being OFF, but the windshield wipers are ON. The dash integration module (DIM) provides battery positive voltage to the signal circuits of the headlamp switch. The signal circuits include the head lamp switch input, and the flash to pass switch.
With the headlamp switch in the ON position, the headlamps on signal circuit is grounded through the headlamp switch to G200. In response to this input, the DIM provides ground to the HDLP LO BM relay control circuit. The IPC illuminates the LIGHTS ON indicator when the DIM detects that the headlamps are requested. When the headlamp dimmer switch lever is pushed away from the driver to the HIGH BEAM position, the HDLP HI BM relay has ground through the headlamp dimmer switch. This Illuminates the high beam headlamps in addition to the low beams. The IPC illuminates the high beam indicator when the DIM detects that the high beam headlamps are requested. The DIM supplies battery positive voltage to the relay coil circuits, if the headlamps are necessary. The underhood fuse block supplies battery positive voltage to both relay switch circuits. When the low beam relay coil is energized, current flows through the HDLOBML fuse and the HDLOBMR fuse to the low beam headlamps. The headlamps have ground at G401. When the HDLP HI BM relay coil is energized, current flows through the HDHIBML fuse and the HDHIBMR fuse to the high beam headlamps. The high beam circuit is divided into a left and right side circuit. The current flow of the left high beam is from the fuse to the left high beam lamp. From the lamp, the current flows to the normally-closed contact of the daytime running lamp (DRL) relay to G104. The current flow of the right high beam is from the fuse to the right high beam headlamp. From the lamp, the current flow is to ground at G401. When the headlamp dimmer switch lever is pulled toward the driver, the flash-to-pass switch closes. This grounds the DIM flash-to-pass input. In response to this input, the DIM energizes the high beam relay. Both high beams remain on until the driver releases the switch handle. If the low beam headlamps were on during flash-to-pass operation, the low beams remain ON.
Headlamps W/high Intensity Discharge (HID)
Normal operation of the HID system starts at the ballast. The headlamp ballast input connector receives the headlamp low beam supply voltage, which would normally be used to directly supply the low beam headlamp. Each ballast has a separate ground at G104. 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. -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 DIM monitors the vehicle's 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, whether manually or automatically the DIM will turn ON the high beam headlamps by activating it's High Beam output.
When the system voltage drops below 8.5 volts, the following will occur:
- STAGE 2: If the low beam headlamps are currently on, whether manually or automatically the DIM will turn OFF the low beam headlamps by deactivating it's Low Beam output.
- If the headlamps are turned on manually, the manual switch redundancy will cause the low beam headlamps to remain on.
- If the headlamp dimmer switch is in the HIGH BEAM position, the low beam headlamps will remain on. The DIM's High Beam output will apply ground through the high beam contact of the headlamp dimmer switch to the low beam relay coil.
If during the same ignition cycle, the DIM enters either STAGE 1 or STAGE 2 operations noted above, then determines that the system voltage has risen, the following will occur:
- If the DIM has entered STAGE 2 operation, it will not return to STAGE 1 operation until the system voltage rises above 9.4 volts.
- If the DIM has entered STAGE 1 operation, it will not return to normal operation until the system voltage rises above 9.8 volts.
Electrical System Requirements (W/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 Lamp (W/HID)
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% 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 such a short period of time. The 75 watt power level allows the lamp to meet the SAE light vs. time specification.
When To Change The Hid Bulb
Bulb failure (end of life) 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 seconds. 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 amp). 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:
- A flickering light, caused in the early stages of bulb failure
- The 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 ballast's 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)
White light has 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. Difference in color is normal. Replace the arc tube only if the arc tube is determined to be at the bulb failure stage.