DIAGNOSIS AND SERVICE The first ste

DIAGNOSIS AND SERVICE The first step when diagnosing an
AFS fault is to perform the following visual inspection.
{ Start by checking that the AFS is switched on. Most AFS
headlights are equipped with a switch that allows the driver to
turn the system on and off. b SEE FIGURE 56 26.
{ 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.
Always follow the recommended testing and service
procedures as specified by the vehicle manufacturer in service
information.
TECH TIP
Checking a Dome Light Can Be Confusing
If a technician checks a dome light with a test light, both
sides of the bulb will turn on the light if the bulb is good.
This will be true if the system s ground switched doors
are closed and the bulb is good. This confuses many
technicians because they do not realize that the ground
will not be sensed unless the door is open.
COURTESY LIGHTS
Courtesy light is a generic term primarily used for interior lights,
including overhead (dome) and under-the-dash (courtesy) lights.
These interior lights are controlled by operating switches located
in the doorjambs of the vehicle doors or by a switch on the dash.
b SEE FIGURE 56 29.
Many Ford vehicles use the door switches to open and close
the power side of the circuit. Many newer vehicles operate the interior
lights through the vehicle computer or through an electronic
module. Because the exact wiring and operation of these units differ,
consult the service information for the exact model of the vehicle
being serviced.
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.
Vehicles equipped with body computers use the input from the key
fob remote to wake up the power supply for the body computer.
DAYTIME RUNNING LIGHTS
PURPOSE AND FUNCTION Daytime running lights (DRLs)
involve operation of the following:
{ Front parking lights
{ Separate DRL lamps
{ Headlights (usually at reduced current and voltage) when the
vehicle is running
Canada has required daytime running lights on all new vehicles
since 1990. Studies have shown that DRLs have reduced accidents
where used.
Daytime running lights primarily use a control module that turns
on either the low or high-beam headlights or separate daytime running
lights. The lights on some vehicles come on when the engine
starts. Other vehicles will turn on the lamps when the engine is running
but delay their operation until a signal from the vehicle speed
sensor indicates that the vehicle is moving.
To avoid having the lights on during servicing, some systems
will turn off the headlights when the parking brake is applied and
the ignition switch is cycled off then back on. Others will only
light the headlights when the vehicle is in a drive gear. b SEE
FIGURE 56 27.CAUTION: Most factory daytime running lights operate the
headlights at reduced intensity. These are not designed to
be used at night. Normal intensity of the headlights (and
operation of the other external lamps) is actuated by turning
on the headlights as usual
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. These strands of plastic are commonly
used in automotive applications as indicators for the driver
that certain lights are functioning. For example, some vehicles are
equipped with fender-mounted units that light when the lights or
turn signals are operating. Plastic fiber-optic strands, which often
look like standard electrical wire, transmit the light at the bulb to
the indicator on top of the fender so that the driver can determine if
a certain light is operating. Fiber-optic strands also can be run like
wires to indicate the operation of all lights on the dash or console.
Fiber-optic strands are also commonly used to light ashtrays, outside
door locks, and other areas where a small amount of light is
required. The source of the light can be any normally operating light
bulb, which means that one bulb can be used to illuminate many
areas. A special bulb clip is normally used to retain the fiber-optic
plastic tube near the bulb.