Had on odd thing happen yesterday. Stopped for fuel and my 13 yr old got out and pumped it. I didn't realize it yet, but he had left the cap off and the fuel door open. He got back in, I started the truck, and as soon as I put it in drive, the horn started blowing and the security led was flashing. It stopped when I got out and put the cap back on. What the heck was that? I've never noticed anything around the filler neck that could send any kind of signal to the ecm or anything. Going to look closer on day this week. Maybe someone other than me can attempt to explain this.

 

Probably a sensor in the tank that can tell by the internal pressure that the cap was left off.

 

There is no pressure build up since the tank has open vent tubes. Perhaps the boy didn't close his door completely after getting back in.

 

like said above^^^^ diesels do not have an evap purge system to monitor pressure inside the tank. on gassers, the evap purge system monitors pressure inside the tank hence when you leave the gas cap off and the purge system performs a system test and sets a check engine light.

 

is it possible that you hit the panic button on the key when turning it over?? i have hit the lock and unlock buttons when starting the truck. if the buttons are facing down when the key is inserted, it's very easy to hit one of them with your thumb when starting the truck.

 

I might have hit the panic but I don't know for sure. Also, why did it stop when i put the cap back on?

I did get it used, so maybe theres some sort of after market thing on it, but if it is, I haven't seen evidence of it, and it apears that the security system is factory. And if it's still factory, whoever did this did one heck of a job of integrating it in.

As said above, I still have no explination. If I get a chance this evening, I'm going to see if I can make it do it again.

 

Did you put it in drive or reverse, were you wearing you seatbelt, and was the door closed all the way... I know, alot, but possibly the back-up warning?

 

I put it in drive. Not sure if the seatbelt was on, but I've put it in drive many times without the seatbelt on and it didn't do this.

 

If you put it in drive, your seatbelt wasn't fastened and the door wasn't closed all the way, you'll get the horn honk from the safety warning that the truck isn't in park. It's possible this is what happened. Although I'm not sure that it checks the passenger door, thought it was just the driver's door.

 

Drivers door never opened at this stop

 

Since it was the security light that came on my bet is that there is a switch on the fuel door mechanism. Probably behind the panel so you can't see it.

Why not open the fuel door and check it again to see if the same thing happens?

 

I forgot to put my cap back on over the weekend. Drove for about 30 minutes and no alarm or codes.

Pete