1999 FORD EXPEDITION sensor

How does the air bag supplemental restraint system work?
The air bag SRS is designed to
activate when the vehicle sustains
sufficient longitudinal deceleration
sufficient to cause the sensors to
close an electrical circuit that
initiates air bag inflation.
The fact that the air bags did not
inflate in a collision does not mean
that something is wrong with the
system. Rather, it means the forces
were not of the type sufficient to
cause activation. Air bags are designed to inflate in frontal and
near-frontal collisions, not rollover, side-impact, or rear-impacts.
The air bags inflate and deflate
rapidly upon activation. After air bag
deployment, it is normal to notice a
smoke-like, powdery residue or
smell the burnt propellant. This may
consist of cornstarch, talcum
powder (to lubricate the bag) or
sodium compounds (e.g., baking
soda) that result from the
combustion process that inflates the
air bag. Small amounts of sodium
hydroxide may be present which
may irritate the skin and eyes, but
none of the residue is toxic.
While the system is designed to help
reduce serious injuries, it may also
cause minor burns, abrasions, swelling or temporary hearing loss.
Because air bags must inflate rapidly and with considerable force, there
is the risk of death or serious injuries such as fractures, facial and eye
injuries or internal injuries, particularly to occupants who are not
properly restrained or are otherwise out of position at the time of air bag
deployment. Thus, it is extremely important that occupants be properly
restrained as far away from the air bag module as possible while
maintaining vehicle control.
Seating and safety restraints
91

Several air bag system components get hot after inflation. Do not
touch them after inflation.
If the air bag is deployed,the air bag will not function again
and must be replaced immediately.If the air bag is not
replaced, the unrepaired area will increase the risk of injury in a
collision.
The SRS consists of:
²driver and passenger air bag modules (which include the inflators and
air bags),
²one or more impact and safing sensors,
²a readiness light and tone
²and the electrical wiring which connects the components.
The diagnostic module monitors its own internal circuits and the
supplemental air bag electrical system warning (including the impact
sensors), the system wiring, the air bag system readiness light, the air
bag back up power and the air bag ignitors.
Determining if the system is operational
The SRS uses a readiness light in the instrument cluster or a tone to
indicate the condition of the system. Refer to theAir bag readiness
section in theInstrumentationchapter. Routine maintenance of the air
bag is not required.
A difficulty with the system is indicated by one or more of the following:
²The readiness light will either
flash or stay lit.
²The readiness light will not
illuminate immediately after ignition is turned on.
²A series of five beeps will be heard. The tone pattern will repeat
periodically until the problem and light are repaired.
If any of these things happen, even intermittently, have the SRS serviced
at your dealership or by a qualified technician immediately. Unless
serviced, the system may not function properly in the event of a
collision.
Seating and safety restraints
92

The fuses are coded as follows.
Fuse/Relay
LocationFuse Amp
RatingDescription
1 25A Audio
2 5A Overhead Trip Computer, Electronic
Automatic Temperature Control (EATC),
Powertrain Control Module (PCM), Cluster
3 20A Cigar Lighter, OBD-II Scan Tool Connector
4 15A Autolamp Module, Remote Entry Module,
Mirrors, Air Suspension Switch
5 15A AC Clutch Relay, Speed Control Module,
Reverse Lamp, EVO Module, Climate Mode
Switch (Front Blower Relay), Daytime
Running Lamp Relay
6 5A Cluster, Overhead Trip Computer, Compass,
Brake Shift Interlock Solenoid, Air
Suspension Module, GEM Module, EVO
Steering Sensor
FUSE1 12 22
21323
617 27
718 28
819 29
930
20
31 21 11 10
RELAY
5 RELAY
4 RELAY
3 RELAY
2 RELAY
1
31424
41525
51626
Roadside emergencies
131

Fuse/Relay
LocationFuse Amp
RatingDescription
12 10A* Rear Wipers
13 Ð Not Used
14 Ð Not Used
15 10A* Running Board Lamps
16 Ð Not Used
17 Ð Not Used
18 15A* Powertrain Control Module, Fuel Injectors,
Fuel Pump, Mass Air Flow Sensor
19 10A* Trailer Tow Stop and Right Turn Lamp
20 10A* Trailer Tow Stop and Left Turn Lamp
21 Ð Not Used
22 Ð Not Used
23 15A* Powertrain Control Module, HEGO Sensors,
Canister Vent
24 15A* Powertrain C ontrol Module, Automatic
Transmission, CMS Sensor
101 30A** Trailer Tow Battery Charge
102 50A** Four Wheel Antilock Brake Module
103 50A** Junction Block Battery Feed
104 30A** 4x4 Shift Motor & Clutch
105 40A** Climate Control Front Blower
106 Ð Not Used
107 Ð Not Used
108 30A** Trailer Tow Electric Brake
109 50A** Air Suspension Compressor
110 30A** Moonroof, Flip Windows and Heated Seats
111 50A** Ignition Switch Battery Feed (Start Circuit)
112 30A** Drivers Power Seat, Adjustable Pedals
113 50A** Ignition Switch Battery Feed (Run and
Accessory Circuits)
114 30A** Climate Control Auxiliary Blower
115 Ð Not Used
Roadside emergencies
135