This is a dangerous job! You need to get a pro to do this. As professional myself, have even had a recent episode with an airbag system. While replacing an airbag control module on a 2005 Explorer, the new control module was defective right out of the box. I did not know it was defective, and when I reactivated the system, the airbag light came on. When I used the scan tool to try and scan the module to find out why the light was on, all the air bags deployed! I nearly came out of my pants! I couldn't catch my breath for several minutes! I am thankful that I was crouched down on the vehicle floor near the console at the time, or I may not still be around. That was an event I will never forget! I got on the phone to Ford, and they told me that I wasn't the first to have that happen! They told me that sometimes a faulty airbag control module will set off the airbags for no reason.
Now I will tell you what 13 means, so that you know when the shop is telling you right. It means that the internal fuse link inside of the air bag control module is blown. You most likely have a short somewhere in the air bag deployment (or firing) circuit that caused it. The internal fuse is not replaceable, so at the very least, you will need a module, but the system needs to be checked for a possible short in the air bag deployment circuit.
Please do not mess with this yourself. Especially this problem! Checking the airbag system requires deactivation of the airbag system, and special airbag simulators installed in place of the airbags themselves. Messing with the deployment circuit especially, can cause death. If the air bag deploys while your head is level with the steering wheel, your neck can be easly broken. An airbag fully inflates, and starts to deflate in less than 4 milliseconds. That is 4 one-thousandths of a second! That is too fast for anyone to get out of the way, and it will injure you. It will literally be like getting hit in the head with a sledge hammer at full speed. These things are dangerous. Most technicians refuse to work on these things. I am one of the few crazy people that will. But I am respectful of them. These things are explosive devices, and I am kind of like the dynamite handler at the rock quarry. A little crazy, but careful. But even as careful as I am, and in spite of my having handled airbags as long as they have been around, back in the '80's, bad things still happen.