I am not referring to the battery in the key fob. My 2007 F150 has the fob and key separate. Mine look like this:


I had 2 keys+fobs and programmed a third key and fob. Then one of my keys stopped working. It is probably one of the original two, but I can't be absolutely sure. The attached fob operates windows and alarm as usual, but when its attached key is inserted, the anti-theft light starts flashing quickly, and engine will not start. A scan showed illegal key inserted.

Let me set definitions:
1) good key and good fob = working original combination
2) bad key and bad fob = non-working original combination
Those name assignments do not change when fobs and keys are exchanged.

After some head scratching, I swapped the fobs. The good key with the bad fob worked perfectly. The bad key with the good fob did not work and gave the illegal code and rapid anti-theft light.

A quick internet search revealed some similar problems that were "fixed" by shifting into neutral. It is claimed that a "Park" detector circuit is to blame. That advice did not help me. Neutral behaved the same.

The keys look identical. My conclusion is that the Ford key is not entirely dumb. What is in the key (like an RFID label or passive transponder?) and can it be fixed?

John

Added FWIW: I examined fob's chip: AN30NT02, which apparently is a PIC12F629/675 or compatible chip. There are even pogo pads to the programming and power pins on its PCB.

BTW: I introduced this topic as an OT comment in another thread. Then continued OT here: https://forum.allaboutcircuits.com/threads/my-2007-f-150-sparkplugs.151791/
However, the problem has now reached the point that I would like to solve it.

MODS: If you want to move that last OT thread here and combine, that is fine with me. I would have done that myself but couldn't. However, I have given enough information above to pinpoint this evolved and distinctly different issue. Staying in automotive section may be better for responses.

 

My 2001 key still works.

As far as I know, there is nothing in the fob that does anything other than operate the locks and alarm, and the head of the key itself contains the "transponder."

Experiments:

• keep your working fob far away while you try your working key
• make a snug fitting tinfoil hat for your working key and see if it still works

 

You are right, the key works without the fob. That is like my 2000 Accord was. I was thinking (incorrectly) that the key and fob had to be paired. I need to see if the key per se can be programmed the same way the fobs were programmed.

Thanks.

John

 

(SOLVED)
I followed two procedures from the internet for the key per se. Neither worked.

I then took a chance and entered program mode by switching on, off x8 ending in "on" with a good key. Pressed a fob button for each fob. Then insert the bad key and repeated getting into program mode. (Or some combination of that -- didn't keep track), but miraculously, all three keys started to work -- at least for now.

In conclusion, I am not sure of the exact sequence used, but as I had 2 working keys and 3 working fobs, I took a chance.