OBJECTIVES After studying Chapter 22, the reader should be able to:

OBJECTIVES After studying Chapter 22, the reader should be able to:
Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “E” (Lighting System Diagnosis and Repair). Determine which replacement bulb to use on a given vehicle. Describe how interior and exterior lighting systems work. Read and interpret a bulb chart. Discuss troubleshooting procedures for lighting and signaling circuits.

LIGHTING The headlight switch controls the following lights on most vehicles: 1. Headlights 2. Taillights 3. Side-marker lights 4. Front parking lights 5. Dash lights 6. Interior (dome) light(s)

BULB NUMBERS Amber-color bulbs that use natural amber glass are indicated with an “NA” for natural amber at the end of the number (for example, 1157NA). A less expensive amber bulb that uses painted glass is labeled “A” for amber (for example, 1157A). FIGURE 22-1 Bulbs that have the same trade number have the same operating voltage and wattage. The NA means that the bulb uses a natural amber glass ampoule with clear turn single lenses.

BULB NUMBERS The amount of light produced by a bulb is determined by the resistance of the filament wire, which also affects the amount of current (in amperes) required by the bulb. FIGURE 22-2 This single-filament bulb is being tested with a digital multimeter set to read resistance in ohms. The reading of 1.3 ohms is the resistance of the bulb when cold. As soon as current flows through the filament, the resistance increases about 10 times. It is the initial surge of current flowing through the filament when the bulb is cool that causes many bulbs to fail in cold weather as a result of the reduced resistance. As the temperature increases, the resistance increases.

BULB NUMBERS FIGURE 22-3 Close-up of a dual-filament (double-filament) bulb (1157) that failed. Notice that one filament (top) broke from its mounting and melted onto the lower filament. This bulb caused the dash lights to come on whenever the brakes were applied.

BULB NUMBERS The correct replacement bulb for a vehicle is usually listed in the owner’s manual or service manual. FIGURE 22-4 Bulbs 1157 or 2057 are typically used for taillight and front parking lights. These bulbs contain both a low-intensity filament for taillights or parking lights and a high-intensity filament for brake lights and turn signals.

BULB NUMBERS

WEIRD PROBLEM—EASY SOLUTION
A General Motors minivan had the following electrical problems. The turn signals flashed rapidly on the left side. With the ignition key off, the lights-on warning chime sounded if the brake pedal was depressed. When the brake pedal was depressed, the dome light came on.

All of these problems were caused by one defective 2057 dual-filament bulb. FIGURE 22-5 Corrosion caused the two terminals of this dual-filament bulb to be electrically connected.

Apparently, the two filaments were electrically connected through the corrosion observed between the terminals of the bulb. This caused the electrical current to feed back from the brake light filament into the taillight circuit, causing all the problems. FIGURE 22-6 Often the best diagnosis is a thorough visual inspection. This bulb was found to be filled with water, which caused weird problems.

BRAKE LIGHTS The brake light switch is a normally open (N.O.) switch but is closed when the driver depresses the brake pedal. The brake switch is also used as an input switch (signal) for the following: 1. Cruise control (deactivates when the brake pedal is depressed) 2. Antilock brakes (ABS) 3. Brake shift interlock (prevents shifting from “park” position unless the brake pedal is depressed)

NO CRUISE CONTROL? CHECK THE THIRD BRAKE LIGHT
A common cause of an inoperative cruise control, especially on General Motors vehicles, is a burned out bulb in the third stop light. The cruise control uses the filaments of the third brake bulb (CHMSL) as a ground and shuts off the cruise if the bulbs are burned out (open).

NO CRUISE CONTROL? CHECK THE THIRD BRAKE LIGHT
FIGURE 22-7 Typical brake light and taillight circuit showing the brake switch and all of the related circuit components.

HEADLIGHT SWITCHES A circuit breaker is built into most headlight switches to protect the headlight circuit. FIGURE 22-8 Typical headlight circuit diagram. Note that the headlight switch is represented by a dotted outline indicating that other circuits (such as dash lights) also operate from the switch.

HEADLIGHT SWITCHES Removing a Headlight Switch
Most dash-mounted headlight switches can be removed by first removing the dash panel. Other headlight switch knobs are removed by depressing a spring-loaded release, which allows for removal of the entire headlight switch knob and shaft.

HEADLIGHT SWITCHES Removing a Headlight Switch
FIGURE 22-9 To remove the headlight switch from a vehicle that uses a knob and shaft, a release button has to be pushed to release the shaft. After the knob and shaft assembly has been removed, then the retaining nut can be removed from the headlight switch so it can be removed from the dash.

SEALED-BEAM HEADLIGHTS
If either the high-beam or the low-beam filament is burned out, the ohmmeter will indicate infinity (OL). FIGURE Typical headlight socket connections. Some vehicles may be different. The high- and low-beam connections must be determined by visual inspection.

HEADLIGHT AIMING According to U.S. federal law, all headlights, regardless of shape, must be able to be aimed using headlight aiming equipment. FIGURE All vehicles sold in the United States must have provision for the use of mechanical aiming devices. Even the halogen bulb units with plastic or glass lenses have locating points and adjustment screws.

HEADLIGHT AIMING FIGURE Typical headlight-aiming diagram as found in a service manual.

HEADLIGHT AIMING FIGURE Many composite headlights have a built-in bubble level to make aiming easy and accurate.

COMPOSITE HEADLIGHTS Composite headlights are constructed using a replaceable bulb and a fixed lens cover that is part of the vehicle. FIGURE A typical composite headlamp assembly. The lens, housing, and bulbs sockets are usually included as a complete assembly.

HALOGEN SEALED-BEAM HEADLIGHTS
Halogen sealed-beam headlights are brighter and more expensive than normal headlights. Because of their extra brightness, it is common practice to have only two headlights on at any one time, because the candlepower output would exceed the maximum U.S. federal standards if all four halogen headlights were on.

DIAGNOSE BULB FAILURE Some causes for halogen bulb failure and their indications are as follows: Gray color—low voltage to bulb (check for corroded socket or connector) White (cloudy) color—indication of an air leak Broken filament—usually caused by excessive vibration Blistered glass—indication that someone has touched the glass

DIAGNOSE BULB FAILURE FIGURE Notice the broken filament in this halogen headlight bulb.

HIGH-INTENSITY DISCHARGE HEADLIGHTS Parts and Operation
High-intensity discharge (HID) headlights produce a distinctive blue-white light that is crisper, clearer, and brighter than light produced by a halogen headlight. The HID lighting system consists of the discharge arc source, igniter, ballast, and headlight assembly. FIGURE The ignitor contains the ballast and transformer needed to provide high-voltage pulses to the arc tube bulb.

The color of light is expressed in temperature using the Kelvin scale. Typical color temperatures include: Daylight—5,400°K HID—4,100°K Halogen—3,200° Incandescent (tungsten)—2,800°K

The HID ballast is powered by 12 volts from the headlight switch on the body control module. The HID headlights operate in three stages or states. 1. Start-up or stroke state 2. Run-up state 3. Steady state FIGURE HID (xenon) headlights emit a whiter light than halogen headlights and usually look blue compared to the parking light on the side.

HIGH-INTENSITY DISCHARGE HEADLIGHTS Start-Up or Stroke State
When the headlight switch is turned to the on position, the ballast may draw up to 20 amperes at 12 volts. The increased voltage is used to create an arc between the electrodes in the bulb.

HIGH-INTENSITY DISCHARGE HEADLIGHTS Run-Up State
After the arc is established, the ballast provides a higher than steady state voltage to the arc tube to keep the bulb illuminated. On a cold bulb, this state could last as long as 40 seconds. On a hot bulb, the run-up state may last only 15 seconds.

HIGH-INTENSITY DISCHARGE HEADLIGHTS Steady State
The steady state phase begins when the power requirement of the bulb drops to 35 watts. The ballast provides a minimum of 55 volts to the bulb during steady state operation.

HIGH-INTENSITY DISCHARGE HEADLIGHTS Failure Symptoms
The following symptoms indicate bulb failure. A flickering light The lights go out (which is caused when the ballast assembly detects repeated bulb restrikes) Color change to a dim pink glow

HIGH-INTENSITY DISCHARGE HEADLIGHTS Diagnosis and Service
High-intensity discharge headlights will change slightly in color with age. This color shift is usually not noticeable unless one headlight arc tube assembly has been replaced due to a collision repair, and then the difference in color may be noticeable.

ADAPTIVE FRONT LIGHTING SYSTEM Parts and Operation
A system that mechanically moves the headlights to follow the direction of the front wheels is called adaptive (or advanced) front light system, or AFS. FIGURE Adaptive front lighting systems rotate the low-beam headlight in the direction of travel.

AFS is often used in addition to self-leveling motors so that the headlights remain properly aimed regardless of how the vehicle is loaded. Without self-leveling, headlights would shine higher than normal if the rear of the vehicle is heavily loaded.

FIGURE A typical adaptive front lighting system uses two motors—one for the up and down movement and the other for rotating the low-beam headlight to the left and right.

ADAPTIVE FRONT LIGHTING SYSTEM Diagnosis and Service
The first step when diagnosing an AFS system fault is to perform the following visual inspection. Start by checking that the AFS system is switched on. Most AFS headlight systems are equipped with a switch that allows the driver to turn the system on and off. FIGURE Typical dash-mounted switch that allows the driver to disable the front lighting system.

ADAPTIVE FRONT LIGHTING SYSTEM Diagnosis and Service
Check that the system performs a self-test during start-up. Verify that both low-beam and high-beam lights function correctly. The system may be disabled if a fault with one of the headlights is detected. Use a scan tool to test for any AFS-related diagnostic trouble codes. Some systems allow the AFS to be checked and operated using a scan tool.

DAYTIME RUNNING LIGHTS
Daytime running lights (DRLs) involve operating front parking lights or the headlights (usually at reduced current and voltage) when the vehicle is running. To avoid having the lights on during servicing, some systems will turn off the headlights when the parking brake is applied.

DAYTIME RUNNING LIGHTS
FIGURE Typical daytime running light (DRL) circuit. Follow the arrows from the DRL module through both headlights. Notice that the left and right headlights are connected in series, resulting in increased resistance, less current flow, and dimmer than normal lighting. When the normal headlights are turned on, both headlights receive full battery voltage, with the left headlight grounding through the DRL module.

DIMMER SWITCHES The headlight switch controls the power or hot side of the headlight circuit. The current is then sent to the dimmer switch, which allows current to flow to either the high-beam or the lowbeam filament of the headlight bulb, To replace most of these types of dimmer switches, the steering column needs to be lowered slightly to gain access to the switch itself, which is also adjustable for proper lever operation.

DIMMER SWITCHES FIGURE Most vehicles use positive switching of the high- and low-beam headlights. Notice that both filaments share the same ground connection. Some vehicles use negative switching and place the dimmer switch between the filaments and the ground.

STOP LAMP AND TURN SIGNALS
When the brakes are applied, the brake switch is closed and the stop lamps light. The brake switch receives current from a fuse that is hot all the time. FIGURE The brake lights are powered directly from the brake switch on a vehicle that uses separate bulbs for brake lights and turn signals.

The turn signal switch is mounted within the steering column and operated by a lever. FIGURE The typical turn signal switch includes various springs and cams to control the switch and to cause the switch to cancel after a turn has been completed.

In systems using separate filaments for the stop and turn lamps, the brake and turn signal switches are not connected. If the vehicle uses the same filament for both purposes, then brake switch current is routed through contacts within the turn signal switch. FIGURE When the stop lamps and turn signals share a common bulb filament, stop light current flows through the turn signal switch.

By linking certain contacts, the bulbs can receive either brake switch current or flasher current, depending upon which direction is being signaled. FIGURE When a right turn is signaled, the turn signal switch contacts send flasher current to the right-hand filament and brake switch current to the left-hand filament.

Aftermarket replacement LED bulbs that are used to replace conventional bulbs may require the use of a different type of flasher unit due to the reduced current draw of the LED bulbs. FIGURE A replacement LED taillight bulb is constructed of many small individual light-emitting diodes.

FLASHER UNITS A turn signal flasher unit is a metal or plastic can containing a switch that opens and closes the turn signal circuit. FIGURE Two styles of two-prong flashers.

FLASHER UNITS Bimetallic flashers
Bimetallic flashers units were the first type used and have generally been replaced with other types that have a longer service life. If one bulb burns out, either in the front or rear of the vehicle, the flasher will not flash on the side with the bad bulb.

FLASHER UNITS Hybrid Flasher (Flasher relay)
A hybrid flasher, also called a flasher relay, is a type of flasher unit that contains an electronic timing circuit and a mechanical relay which opens and closes the turn signal circuit. If all bulbs are burned out, the flasher will not flash at all.

FLASHER UNITS Solid-State Flashers
Solid state flashers use an electronic switching circuit and an electronic timing circuit to operate the turn signals. Because these units do not use a mechanical switch or contacts to open and close the turn signal circuit, these flashers last a long time, but cost more than bimetallic or hybrid units.

FLASHER UNITS Hazard Warning Flasher
A typical hazard warning flasher is also called a parallel or variable-load flasher because there is a resistor in parallel with the contacts to provide a control load and, therefore, a constant flash rate, regardless of the number of bulbs being flashed. FIGURE A hazard flasher uses a parallel resistor across the contacts to provide a constant flashing rate regardless of the number of bulbs used in the circuit.

FLASHER UNITS Combination Turn Signal and Hazard Warning Flasher
The combination flasher is a device which combines the functions of a turn signal flasher and a hazard warning flasher into one package.

FLASHER UNITS Electronic Flasher Replacement Units
Older vehicles (and a few newer ones) use thermal (bimetal) flashers that use heat to switch on and off. Newer vehicles use electronic flashers that use microchips to control the on/off function.

FLASHER UNITS Electronic Flasher Replacement Units
Other common turn signal problems and possible solutions include the following:

WHY DOES THE SIDE-MARKER LIGHT ALTERNATELY FLASH?
The side marker light goes out when the lights are on and the turn signal is flashing because there are 12 volts on both sides of the bulb. FIGURE The side-marker light goes out when there is voltage at both points X and Y. These opposing voltages stop current flow through the side-marker light. The left turn light and left park light are actually the same bulb (usually a 2057) and are shown separately to help explain how the side-marker light works on many vehicles.

COURTESY LIGHTS Courtesy light is a generic term primarily used for interior lights, including overhead (dome) and under-the-dash (courtesy) lights. FIGURE A typical courtesy light doorjamb switch. Newer vehicles use the door switch as an input to the vehicle computer and the computer turns on or off the interior lights. By placing the lights under the control of the computer, the vehicle engineers have the opportunity to delay the lights after the door is closed and to shut them off after a period of time to avoid draining the battery.

ILLUMINATED ENTRY Some vehicles are equipped with illuminated entry, meaning the interior lights are turned on for a given amount of time when the outside door handle is operated while the doors are locked. Most vehicles equipped with illuminated entry also light the exterior door keyhole.

FIBER OPTICS Fiber optics is the transmission of light through special plastic (polymethyl methacrylate) that keeps the light rays parallel even if the plastic is tied in a knot. The source of the light can be any normally operating light bulb, which means that one bulb can be used to illuminate many areas.

AUTOMATIC DIMMING MIRRORS Parts and Operation
Automatic dimming mirrors use electrochromic technology to dim the mirror in proportion to the amount of headlight glare from other vehicles at the rear. If automatic dimming mirrors are used on the exterior, the sensors in the interior mirror and electronics are used to control both the interior and exterior mirrors.

AUTOMATIC DIMMING MIRRORS Diagnosis and Service
If a customer concern states that the mirrors do not dim when exposed to bright headlights from the vehicle behind, the cause could be sensors or the mirror itself. One typical fault that can occur to automatic dimming mirrors is that a crack can occur in the mirror assembly allowing the gel to escape from between the two layers of glass.

FEEDBACK When current that lacks a good ground goes backward along the power side of the circuit in search of a return path (ground) to the battery, this reverse flow is called feedback or reverse-bias current flow. Feedback can cause other lights or gauges that should not be working to actually work.

FEEDBACK Feedback Example
A customer complained that when the headlights were on, the left turn signal indicator light on the dash remained on. The cause was found to be a poor ground connection for the left front parking light socket. Cleaning or replacing the socket usually solves the problem if the ground wire for the socket is making a secure chassis ground connection.

LIGHTING SYSTEM SYMPTOM GUIDE
The following list will assist technicians in troubleshooting lighting systems.

TAILLIGHT BULB REPLACEMENT Step-by-Step

TAILLIGHT BULB REPLACEMENT Step-by-Step cont

OPTICAL HEADLIGHT AIMING Step-by-Step

OPTICAL HEADLIGHT AIMING Step-by-Step cont

SUMMARY Automotive bulbs are identified by trade numbers.
The trade number is the same regardless of manufacturer for the exact same bulb specification. Daytime running lights (DRLs) light the headlights, usually at reduced intensity, when the engine is running or the vehicle is moving. High-intensity discharge (HID) headlights are brighter and have a blue tint. One defective turn signal bulb causes the turn signal on the affected side to stop blinking (flashing).

REVIEW QUESTIONS Explain why the exact same trade number of bulb should be used as a replacement. Explain why you should not touch a halogen bulb with your fingers. Describe how to diagnose a turn signal operating problem. Discuss how to aim headlights on a vehicle equipped with aerodynamic-style headlights.

CHAPTER QUIZ Technician A says that the bulb trade number is the same for all bulbs of the same size. Technician B says that a dual-filament bulb has different candlepower ratings for each filament. Which technician is correct? Technician A only Technician B only Both Technicians A and B Neither Technician A nor B

CHAPTER QUIZ 2. Two technicians are discussing flasher units. Technician A says that only a DOT-approved flasher unit should be used for turn signals. Technician B says that a parallel (variable-load) flasher will function for turn signal usage, although it will not warn the driver if a bulb burns out. Which technician is correct? Technician A only Technician B only Both Technicians A and B Neither Technician A nor B

CHAPTER QUIZ 3. Interior overhead lights (dome lights) are operated by door jamb switches that _____. Complete the power side of the circuit Complete the ground side of the circuit Move the bulb(s) into contact with the power and ground Complete either a or b depending on application

4. Electrical feedback is usually a result of _____.
CHAPTER QUIZ 4. Electrical feedback is usually a result of _____. Too high a voltage in a circuit Too much current (in amperes) in a circuit Lack of a proper ground Both a and b

5. Which bulb is brightest? (see the bulb table)
CHAPTER QUIZ 5. Which bulb is brightest? (see the bulb table) 194 168 194NA 1157

CHAPTER QUIZ 6. If a 1157 bulb were to be installed in a left front parking light socket instead of a 2057 bulb, what would be the most likely result? The left turn signal would flash faster. The left turn signal would flash slower. The left parking light would be slightly brighter. The left parking light would be slightly dimmer.

CHAPTER QUIZ 7. A technician replaced a 1157NA with a 1157A bulb. Which is the most likely result? The bulb is brighter because the 1157A candlepower is higher. The amber color of the bulb is a different shade. The bulb is dimmer because the 1157A candlepower is lower. Both b and c would occur.

CHAPTER QUIZ 8. A customer complained that every time he turned on his vehicle’s lights, the left-side turn signal indicator light on the dash remained on. The most likely cause is _____. A poor ground to the parking light (or taillight) bulb on the left side A poor ground to the parking light (or taillight) bulb on the right side, causing current to flow to the left-side lights A defective (open) parking light (or taillight) bulb on the left side Both a and c

CHAPTER QUIZ 9. A defective taillight or front park light bulb could cause _____. The turn signal indicator on the dash to light when the lights are turned on The dash lights to come on when the brake lightS are on The lights-on warning chime to sound if the brake pedal is depressed All of the above

CHAPTER QUIZ 10.A defective brake switch could prevent proper operation of the _____. Cruise control ABS brakes Shift interlock All of the above

OBJECTIVES After studying Chapter 22, the reader should be able to:

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