What is causing the air bag readiness light to start flashing then stay on in a Ford Expedition?

What is causing the air bag readiness light to start flashing then stay on in a Ford Expedition?
There is a fault some where in the system.Auto Zone will check your codes for FREE.I just don't know if it will pick up the Air bag codes.But since it's FREE you dont have anything to loose but time.Also check this out.Air Bag Codes Here are the codes for Air Bag faults. When first started the dash light will blink the two-digit code before it comes on permently.

Continuous (blinks no code)
RCM Disconnected or Inoperative, Loss of Battery Feed, or Loss of
Signal Ground

15
Incorrect Vehicle ID

15
Driver Air Bag Circuit Shorted To
Ground

15
Driver Air Bag Circuit Shorted To
Battery Or Ignition

16
Passenger Air Bag Circuit Shorted
To Ground

16
Passenger Air Bag Circuit Shorted
To Battery Or Ignition

17
Air Bag Tone Warning Indicator
Circuit Shorted to Ground or Open

17
Driver Pretension Circuit
Shorted To Battery Or Ignition

17
Driver Pretension Circuit
Shorted To Ground

18
Passenger Pretension Circuit
Shorted To Battery Or Ignition

18
Driver Pretension Circuit
Shorted To Ground

18
Air Bag Tone Warning Indicator
Circuit Short to Battery or
Ignition

19
RCM Crash Data Memory Full

21
RCM Bracket Ground Resistance
High

24
RCM Is Faulted

25
Passenger Air Bag Deactivation
(PAD) Switch Fault

27
Passenger Air Bag Deactivation
(PAD) Warning Lamp Inoperative

27
Passenger Air Bag Deactivation
(PAD) Warning Lamp Shorted to
Battery

32
Driver Air Bag Circuit Resistance
High

33
Passenger Air Bag Circuit
Resistance High

34
Driver Air Bag Circuit Resistance
Low

35
Passenger Air Bag Circuit
Resistance Low

46
Driver Pretension Circuit
Resistance High

46
Driver Pretension Circuit
Resistance Low

47
Passenger Pretension Circuit
Resistance High

47
Passenger Pretension Circuit
Resistance Low