Hello,
I too have been very unhappy about the double horn notification that our Explorers exhibit. I read through this complete thread hoping to find a solution to removing this behavior. I obviously didn't find a solution. What I did find was a lot of speculation and flat out misinformation. I hope my explanation about this feature at least gets everyone on the same page as to why this double horn alert is happening.
This feature has nothing to do with NHTSA or another government agency requirements. It is simply a function of warning the driver that the vehicle is running and of the central locking system in conjunction with the "Autolock" feature. In some situations if you turn the "Autolock" feature off, then you will not hear the double horn alert.
A quick explanation of the central locking system. Most likely if you have the "Autolock" feature turned on, you also have the "Autounlock" feature checked. Different auto manufactures handle this feature differently. Personally, I am not a fan of FOMOCO's execution of the "Autounlock" feature. If you have both features turned on what you experience is; Start the vehicle and drive away. Once you reach about 5mph the locks are triggered closed. Now you pull into your driveway, and turn off the car, the locks are triggered opened when you pull the driver door handle. Most German manufactures and some Japanese manufactures use the start/stop button as the trigger. When you turn off the vehicle with the start/stop button, the central locking system unlocks the vehicle. In a minute you will see why this is, in my opinion, a better method.
Ok, now let me outline the situations that will sound the double horn.
1 - Horn alerts when the vehicle is running and you exit and close the door behind yourself. You are being warned that you are walking away from a running vehicle. The double horn will not alert if your key remains in the vehicle when you exit and close the door behind yourself. Your vehicle believes you are still in it, therefore no alert.
2 - Horn alerts when the vehicle is turned off and any occupant other then the driver exits first (my biggest issue & the reason why I am not a fan of Ford's execution of the "Autounlock" feature). This mostly happens when you have a passenger in the front seat. You pull-up and turn off the vehicle. Your passenger jumps out before you and closes their door. You get the alert. Remember the central locking system is triggered open by the driver door handle. When your passenger exits the vehicle, they are manually unlocking their door. When they close their door, the vehicle thinks that you are trying to lock the key in the car and thats the reason for this alert. This alert can also be heard if a person exits the rear doors before the driver, but is less common as the rear passenger must manually pull up the lock wand on the top of the door to exit the vehicle.
There is one interesting item that I would like to point out. If the vehicle is running and you open the tailgate with the dash button, and then step out of the driver door and close it behind you, the alert will not sound. As soon as you close the tailgate, the alert will sound unless you have gotten back in the vehicle before the tailgate closes all the way.
