1994 F150 Beeping when brakes applied/flashing airbag light code 5 1

[sundancepilot]

After driving three hours, we pulled off the interstate and when I applied the brakes, we got a beeping (alarm-type) noise that sounded like it was coming from under the dash or under the seat--it was hard to tell. The noise quit when I released the brake and was intermittent when I applied the brake after that; sometimes it beeped when I put the brakes on and sometimes it didn't. There were no lights associated with the brakes, the ABS or the airbag on the panel.

Ironically, we were pulling into a Ford dealership to buy an Expedition for my wife. I asked the service manager about the noise and he said it might be a brake servo module under the dash. I wasn't able to leave the pickup with them to troubleshoot or fix, so I headed home, about 40 miles.

On the way home, the beeping noise was gone, but the airbag light flashed a 5 1 code continuously.

Any suggestions about a cause for either the beep or the airbag light?
Is it something that I can replace, or should it be taken to a shop?

Thanks,
Ken

[peppermrj]

Here is a link to abs troubleshooting. I wish I knew more but hopefully this will help. Diagnosis and Testing

This link is for the air bag system.
Air Bag Diagnostic Monitor
Use the previous and next arrows in the box for more info.
Good hunting.