How to change the lock code on a 2005 Ford 500?

When I brought the car, the elderly lady couldn't remember the code.

You can't change the security code it is tied to the units serial number printed on the unit itself. Find the serial and re ask and myself or someone else will give it you as long as it starts with "M" if it starts with "V" it is dealer only.

You can't. It can only be done through a Ford main dealer or agency

The Door Lock code is found on your security module. It is located under the dash on the driver side near the fuse box.

Remove the three hex head screws under the front edge of the panel below the steering column. One of the screws is behind the hood release lever. The panel is also attached with clips at the top edge; just pop these out.

The computer module is the same black box that has the fuses -- it says "pull" on the front where you can take the lid off to change fuses. The factory keypad code sticker on our car is on the BACK of the box, near the left side. To see it, I had to partially remove the box.

It's not necessary to unplug any of the cables from the box, but you need to remove the three nuts that secure the box. They are 10mm nuts, & you'll need a deep socket. One nut is at the bottom, one at the top near the upper right corner, and one on the left near the top. That last one is the least accessible, but it's not too difficult.

Get the nuts off, pull the box forwards until you can reach behind it with a small hand mirror to read the code. It's a 5-digit number & should be obvious. The numbers will be backward (in the mirror) and possibly upside down, so note carefully. I had a hard time figuring out whether one digit was a 6 or a 9, so I just tried it both ways, also forwards and backwards, until one of the combinations worked.

Then just replace the nuts & the dash panel, & use the factory code to reprogram the keyless entry code as explained in the manual. Be sure to write down the factory code somewhere safe and pass it along to the next owner if you sell the car.

If you can't find the auto-lock module. Take the vehicle to your local Ford dealer. They are able to scan the vehicle's computer and recover the preset entry code for you. Most will do this for no charge, however, you may be charged their minimum labor charge for the service. Call in advance to know how much it will cost.

Once you have the factory preset code…

Erase all previous Personal Entry Codes
1 Enter the preset entry code.
2 Press and release the "1-2" button within five seconds of entering the preset entry code.
3 Press and hold the "1-2" button for two seconds. You must do this with five seconds of completing the last step.
4 All personal entry codes are now erased. Only the factory preset entry code will open the vehicle.

Enter a new Personal Entry Code
1 Enter the preset entry code (found on your security module)
2 Within five seconds press the "1-2" button on the key pad.
3 Enter your five-digit personal entry code. Each number must be pressed within five seconds of the last.
4 Press the "1-2," "3-4" or "5-6" button to set which of the three personal entry code slots you wish to use. You can program up to three personal entry codes.
5 The doors will lock and then unlock to confirm your entry of a new personal entry code.