1999 GMC SUBURBAN sensor

1-36 Servicing Your Air Bag-Equipped Vehicle
Air bags affect how your vehicle should be serviced.
There are parts of the air bag systems in several places
around your vehicle. Your dealer and the service manual
have information about servicing your vehicle and the
air bag systems. To purchase a service manual, see
ªService and Owner Publicationsº in the Index.
CAUTION:
For up to two minutes after the ignition key is
turned off and the battery is disconnected, an
air bag can still inflate during improper service.
You can be injured if you are close to an air bag
when it inflates. Avoid yellow connectors. They
are probably part of the air bag systems. Be sure
to follow proper service procedures, and make
sure the person performing work for you is
qualified to do so.
The air bag systems do not need regular maintenance.
Adding Equipment to Your Air
Bag-Equipped Vehicle
Q:If I add a push bumper or bicycle rack to the
front of my vehicle, will it keep the air bags
from working properly?
A:As long as the push bumper or bicycle rack is
attached to your vehicle so that the vehicle's basic
structure isn't changed, it's not likely to keep the
air bags from working properly in a crash.
Q:Is there anything I might add to the front or
sides of the vehicle that could keep the air bags
from working properly?
A:Yes. If you add things that change your vehicle's
frame, bumper system, front end or side sheet metal
or height, they may keep the air bag system from
working properly. Also, the air bag system may not
work properly if you relocate any of the air bag
sensors. If you have any questions about this, you
should contact Customer Assistance before you
modify your vehicle. (The phone numbers and
addresses for Customer Assistance are in Step Two
of the Customer Satisfaction Procedure in this
manual. See ªCustomer Satisfaction Procedureº
in the Index.)

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Your vehicle is equipped with a light sensor located on
the top of the instrument panel in the defroster grille. Be
sure it is not covered, or the system will be on whenever
the ignition is on.
The system may also turn on your headlamps when
driving through a parking garage, heavy overcast
weather or a tunnel. This is normal.
There is a delay in the transition between the daytime
and nighttime operation of the Daytime Running
Lamps (DRL) and the automatic headlamp systems
so that driving under bridges or bright overhead street
lights does not affect the system. The DRL and
automatic headlamp system will only be affected when
the light sensor sees a change in lighting lasting longer
than the delay.
To idle your vehicle with the automatic headlamp
system off, set the parking brake while the ignition is
off. Then start your vehicle. The automatic headlamp
system will stay off until you release the parking brake.
As with any vehicle, you should turn on the regular
headlamp system when you need it.
You may be able to turn off your Automatic Headlamp
System. See ªDaytime Running Lamps (DRL)º later in
this section for more information.Lamps On Reminder
A reminder chime will sound when your headlamps or
parking lamps are manually turned on and your ignition
is in OFF, LOCK or ACCESSORY. To disable the
chime, rotate the thumbwheel all the way down. In the
automatic mode, the headlamps turn off once the
ignition key is in OFF.
Daytime Running Lamps
Daytime Running Lamps (DRL) can make it easier for
others to see the front of your vehicle during the day.
DRL can be helpful in many different driving
conditions, but they can be especially helpful in the
short periods after dawn and before sunset.
The DRL system will come on when:

the ignition is on,

the headlamp switch is in automatic headlamp mode,

the automatic transmission is not in PARK (P),

the light sensor determines it is daytime and

the parking brake is released.
When the DRL are on, only your DRL lamps will be on.
The taillamps, sidemarker and other lamps won't be on.
The instrument panel won't be lit up either.

2-70
Waiting to do repairs can be costly -- and even
dangerous. So please get to know your warning lights
and gages. They're a big help.
Your vehicle may also have a driver information system
that works along with the warning lights and gages.
See ªMessage Centerº in the Index.
Safety Belt Reminder Light
When the key is turned to RUN or START, a chime
will come on for about six seconds to remind people to
fasten their safety belts, unless the driver's safety belt is
already buckled.
The safety belt light will
also come on and stay on
for about 20 seconds,
then it will flash for
about 55 seconds.
If the driver's belt is already buckled, neither the chime
nor the light will come on.
Air Bag Readiness Light
There is an air bag readiness light on the instrument
panel, which shows the air bag symbol. The system
checks the air bag's electrical system for malfunctions.
The light tells you if there is an electrical problem.
The system check includes the air bag sensors, the
air bag modules, the wiring and the crash sensing and
diagnostic module. For more information on the air bag
system, see ªAir Bagº in the Index.
This light will come on
when you start your vehicle,
and it will flash for a few
seconds. Then the light
should go out. This means
the system is ready.
If the air bag readiness light stays on after you start the
vehicle or comes on when you are driving, your air bag
system may not work properly. Have your vehicle
serviced right away.

3-5 Electronic Climate Control System
(If Equipped)
Fan Control
The knob on the left side of the electronic climate
control panel controls the fan speed. To manually
increase airflow, move the knob clockwise. To manually
decrease airflow, move it counterclockwise.
OFF: If the knob is in OFF, outside air will still enter
the vehicle, and will be directed based on the position of
the mode knob.
AUTO: If the knob is in AUTO, the fan speed will vary
as the system maintains the selected temperature.When both the Fan Control and Mode Knobs are in
the AUTO position, the system will then automatically
maintain the desired cabin temperature as selected by
Temperature Knob. Manual control of functions is
also available.
Temperature Knob
The middle knob on the control panel lets you select
the desired air temperature in your vehicle. This knob
will allow you to adjust the interior air temperature
independent of the function knob setting. Move the
knob clockwise toward 82 for warmer air. Move the
knob counterclockwise toward 66 for cooler air. When
the system is set for automatic operation, sensors will
control the fan/blower speed.
Full Hot: If you turn the temperature knob past
82
F (28
C), the system will go into the ªfull hotº
mode. The system will remain at that maximum heating
setting and the fan will blow at the speed the fan knob is
set to. If the fan is in AUTO, it will run at full speed.
Full Cold: If you turn the temperature knob past
66
F (19
C), the system will go into the ªfull coldº
mode. The system will remain at that maximum cooling
setting and the fan will blow at the speed the fan knob is
set to. If the fan is in AUTO, it will run at full speed.

3-6
Mode Knob - Automatic Operation
The right knob on the control panel allows you to
choose the direction of air delivery. When the system is
set for automatic operation, sensors will control the air
delivery mode. Air will come primarily from the floor or
instrument panel outlets, with some air directed to the
windshield to prevent fogging.
When the system is in AUTO mode, the air conditioning
light will turn on, and the recirculation and outside air
lights turn off. With the system in full auto control
(both the fan and mode knobs in AUTO), you still
have the ability to override any function. However,
continually overriding the outside air or the A/C
compressor will limit the ability of the system to cool
the vehicle quickly.
If you push a button for a function which is not
available, the light next to that button will flash three
times to alert you that it's not available.
To find your comfort zone, start with the 74
F (23
C)
setting and allow about 20 minutes for the system to
adjust the temperature if necessary.With the automatic setting, the air conditioning
compressor automatically cycles when needed to cool the
air. In cold weather, when the system senses the need
for heat, the airflow will be directed out the floor outlets.
As the interior temperature approaches a desired setting,
the blower speed will decrease. To maintain interior
comfort, the airflow will adjust between the instrument
panel air outlets and floor outlets. On bright sunny days
in cool weather, the airflow may come out of the air
conditioning and floor outlets (bi
-level mode) to maintain
comfort and prevent stuffiness.
To avoid blowing cold air in cold weather, the system
will delay turning on the fan until warm air is available.
The length of delay depends on the outside air
temperature, engine coolant temperature or the time
since the engine was last started. As the coolant warms
up, the blower fan speed will gradually increase and
air will flow from the heater outlets, with some airflow
to the windshield to prevent fogging under most
normal conditions.
Be careful not to put anything over the solar sensor
located around the center of the instrument panel.
This sensor is used by the automatic system to
regulate temperature.

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Name Usage
RR DEFOG Rear Window Defogger,
Heated Mirrors (Relay)
RTD Autoride
(Real Time Damping)
RR PRK Right Rear Parking Lamps
ECM B VCM/PCM
F/PMP Fuel Pump (Relay)
O2 A Oxygen Sensors
O2 B Oxygen Sensors
LR PRK Left Rear Parking Lamps
RR DEFOG Rear Window Defogger,
Heated Mirrors
HDLP Headlamps (Relay)
TRL PRK Parking Lamps Trailer Wiring
PRIME Not Used
RT HDLP Right Headlamps
DRL Daytime Running Lamps (Relay)
HTD MIR Heated Mirrors
LT HDLP Left HeadlampsName Usage
A/C Air Conditioning
AUX PWR Cigarette Lighter, Auxiliary
Power Outlets
SEO 2 Special Equipment Option Power,
Power Seats, Aux Roof Mnt Lamp
SEO 1 Special Equipment Option Power,
Aux Roof Mnt Lamp, Cell Phone
DRL Daytime Running Lamps
A/C A/C (Relay)
FOG LP Fog Lamps
FOG LP Fog Lamps (Relay)
RADIO Audio System, Instrument Cluster,
Climate Control System
CIGAR Cigarette Lighter, Auxiliary
Power Outlets
RT TURN Right Turn Signals
BTSI Automatic Transmission Shift
Lock Control System
LT TURN Left Turn Signals