Spent several hours searching, but haven't found anything similar. Hope someone can help.

I have '04 supercrew 5.4 lariat. Bought new at end of '03. In '06 I started having a weird problems with antitheft system (for instance, if I had the driver's door open and tried to start, it would start for a second, the ignition kill would kick in, and the horn would start honking the panic tones). In addition, I could lock it in the driveway, and 5-10 minutes later the antitheft would kick in and start honking like crazy. At that point, even the keyfob wouldn't stop it. I would have to key in the door pad code to get it to turn off. When these problems started in '06, it lasted for a week or so, and then I startd having trouble starting the truck. At that point, tested battery, and it was bad. Replaced it and no further problems...until last week.

Now, I can no longer leave the truck locked. If I lock it, the antitheft will start honking again, sometimes after a few minutes, sometimes after 30 or 45. In addition, I can't unlock the truck with the key (not the fob, but the actual key) without the horn going crazy. I took battery down for testing today, and it all tested good. Guy at the parts shop suggested the PCM may be bad. This is tremendously frustrating, and I'm taking it in to dealership tomorrow, but thought I'd hit up the forums for advice before I spend too much $$$ or time.

Thanks in advance...

 

I had almost the exact same thing go wrong with my other car (black one in sig). I"m going to say it's the battery.

My battery read 12 volts across the poles and tested just fine, but when I tried using it, the vehicle went haywire. Swapped the battery from my F-150 in and the problem went away.

For S**t's and giggles, I put the battery in my F-150 and it did the same thing. Relays cycling and doorlocks quit working, horn honking.

Ended up that the battery had sufferred an internal cell failure and had reversed polarities.

hope you're luck and it's just a battery

 

any update?