OK, here's the story.

The other day when leaving home I noticed that the airbag light was flashing, after driving 60 miles in the rain I parked the truck, about 2 hours later when returning to it my wife noticed that the headlights were on, I know I turned them off.

The switch was indeed off, I started the truck, no issue there but the lights would not turn off and no parking lights.

Drove home and unhooked the battery.

Today " about 36 hours with battery disconnected " I went to check the fuses and found the one to the trailer pigtail shot, I checked the wires there and found a short and fixed it.

New fuse, start the truck, first I noticed that the OD light was flashing, tried to drive it, appears to be in 2nd " limp home mode ", and missing a bit, AC won't engage.

Pulled the codes and it's showing like 20 immediately after starting.

Cleared the codes and looked everywhere for a short, nada.

I did find some water in the chassis inside the truck by the door on the passenger side near the ECM.

Pulled the ECM out, looked dry.
2001 F150 XLT 4.2 V6

Prior to this it had no codes and ran/drove fine.

I have an Ultraguage on the dash full time and it's set to alarm on codes.

Anyone have any suggestions?

 

What year and model is your truck? We need details, we can't see it through the Internet.

 

My bad, it's a 2001 F150 XLT 4.2 V6

 

OK, think I solved the issue, I decided to go outside and hook the ECM and battery back up and let it sit over nite, hooked it up, ECM is sitting on top the battery.

I decided to look over the trailer pigtail one more time, it still looked fine, decided to start it up and take a pic of all the codes.

After starting " still showing all the same symptoms " I decided to look under the hood one more time, looked at fuses again, thought, why is the AC not working, hey, there's a spot up top that looks like a spare fuse goes, well, when I pulled that spare earlier I actually pulled the fuse for the HEGO Sensor.

The AC engaged when I put that fuse in, so limp home mode disables the AC, makes sense.

I'm glad it's running now with no codes but I will have to reason out the events that lead up to all this.

 

That fuse for the "HEGO sensor", F23 in the underhood fusebox, actually runs most of the sensors and actuators under the hood, hence the long list of fault codes and the limp mode. It also supplies the WOT relay which, if unpowered, keeps the A/C from operating.

 

Fuse 23 was my first guess reading the story of 20 codes all at once.


As for the headlights: that would be the BCM not ECM. Also possible it's bad contacts inside the switch, or something related to DRL circuit if you're equipped for that