Tuesday, 16 November 2010

Repairing a Ford Focus or Mondeo Keyfob Remote

A few months back my father was having trouble with the remote control central locking on his Ford Focus, a new battery in the keyfob didn't help, so I gave the contacts a quick clean with some isopropyl alcohol and all seemed well, until about a month later when it stopped working again. Initially I suspected the cheap 8 for a pound lithium battery I'd used, but realised it was probably a faulty switch after a further replacement only lasted a week, by which time the doors had also started to occasionally relock themselves.

A replacement remote keyfob from Ford, is quite expensive, so he was keen for me to try and fix it.


To get the key apart, use a small screwdriver inserted into the slot at the back to pry the remote section out of the key yoke. The two halves of the remote section then simply unclip.

Should you decide to order a new remote from Ford, you'll find the part number on the remote section just below the slot. The RFID chip, which deactivates the immobiliser appears to be located in the half containing the battery, so if you don't have the two keys required to reprogram the immobiliser to accept the RFID in a new remote, swapping the battery compartment over would probably work.


The plastic cover over the PCB is held in place by a couple of plastic pegs, which have had their ends melted to stop them pulling back through the holes. Rather than cut the melted ends off , I squeezed them around with a pair of tweezers reducing the diameter enough to pop through the hole.

By now I'm wearing an anti-static strap, rather than risking zapping the electronics. They only cost about 2 quid from somewhere like dealextreme, but don't buy "wireless" ones, as they are a con, and don't work.



Gently pop the top peg out of the slot in the PCB to release it.

With the PCB removed, you can see the three miniature switches.

Testing my dad's ones with a meter revealed that the lock button had a partial short, enough to slowly drain the battery, but not normally quite enough to trigger the doors to lock

The cause was corrosion inside the switch, the debris from which, was creating the short. It must have got moisture in, although my dad is certain that the key has never got wet. The key for his previous Focus went through the wash cycle on at least one occasion that I know of, but never developed a fault, the seal on this one clearly isn't so good.

The switches come apart quite easily, by using a jeweller's screwdriver to  pop off their metal shells. They are a miniature leaf switch, one leaf acts as a contact, the other increases the force required to operate it. The one shown on the left was black, but cleaned up quite well

As a temporary fix, I unclipped the metal shells, scraped off the worst of the corrosion from the contacts and the silver plated leaf on each switch with a jeweller's screwdriver, and cleaned them with isopropyl alcohol. This restored the remote to full working order,  if you are lucky that might be all that is needed, but because of the very poor condition of the lock switch, I decided to source some replacements.

The switches are 2 x 6 mm KSR subminiature tactile switches made by C&K. From measuring the pressure required to operate the originals, I reckoned the 4.5N KSR251GLFS is the best match. You might even find you could swap the leaf switch and buttons over, rather than unsoldering the base, providing you can get the contacts in the switch base nice and clean.


I'm afraid I don't have any pictures of soldering the replacement switches  in, as I passed the job on to my brother; he's vastly better at soldering fiddly smt components than me. He tells me that he used a craft knife to separate the solder joints while heating it with his iron.

When you come to soldering the new switches on the solder pads on the switch are gull-winded so should draw  the solder in, the tricky bit is having a steady hand so as not to move them, or if you are clumsy like me, you might find it easier to solder them if you use a plastic spring clip to hold them in place.

After reassembling and testing the key, you should fix the PCB and its cover firmly in place, as even a small amount of play can cause the battery contacts to bend and eventually lose contact with the pads on the PCB when pressing the buttons.. So I'd suggest gluing it in place, or as I have, to make it easy should I ever need to take it apart again, I stuck a small thin square of foam rubber (I used a strip of stick on rubber feet, but  something like draft excluder might be thin enough) on the PCB cover so that it presses on the centre of the battery.

The key is now working fine, and cost less than a tenner to fix,  with a few spare switches left over, should it ever fail again.

22 comments:

nigel vallance said...

fantastic article matey, ive now sorted my key fob, {renault clio} the tiny slivers of metal had fallen out of the switch! i put them back in and hey presto the key works again. i'd tried all sorts, Thanks very much it's great when people share there knowledge with others .
Nige.

nigel vallance said...

fantastic article matey, ive now sorted my key fob, {renault clio} the tiny slivers of metal had fallen out of the switch! i put them back in and hey presto the key works again. i'd tried all sorts, Thanks very much it's great when people share there knowledge with others .
Nige.

Sean Phillips said...

you beauty! my key fob for my mondeo had not worked for 9 months, that is until i followed your instructions. thank you :-)

Sean Phillips said...

you beauty! my key fob for my mondeo had not worked for 9 months, that is until i followed your instructions. thank you :-)

Karen knowles said...

Thanks a million. My switch to open the car was completely broke.The metal shell was missing and I couldn't see any way to fix it. I read your article and swapped it with the switch that opens the boot,as i never use it.It worked,I am over the moon,I have had nothing but trouble with the keys,it cost me £65 last time to re-tune it back in to the immobilizer. Thank you for your information :))

paul swift said...

Cheers young man, switch on mine had come away, read your blog and 5 minutes later job done, thanks for posting the info.

paul swift said...

Cheers young man, switch on mine had come away, read your blog and 5 minutes later job done, thanks for posting the info.

Ben Thorne said...

Just fixed my wife's focus key after the lock switch came off.

You deserve pint!

Gville said...

I agree with all the previous comments, brilliant article, well laid out and extremely helpful.
Sorted my problem out straight away.
Thanks a lot,well deserving of a pint indeed!

Nginmu Mbetse said...

bookmarked. thanks for writing this up matey

Nginmu Mbetse said...
This comment has been removed by the author.
antithematter said...

Just wondering if you would know the part number of the three pin transistor/regulator on the rear of the remote. Just bought an older mondeo and it looks like someone has punctured the plastic casing when trying to change the battery and smashed the part.

Cheers

Leslie Lim said...


First time I commented in a blog! I really enjoy it. You have an awesome post. Please do more articles like this. I'm gonna come back surely. God bless.

Rica
www.imarksweb.org

Tidy C. said...

Thanks !! From Romania .

Komal Singh said...
This comment has been removed by a blog administrator.
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Andre Beluchi said...

Just this morning, my wife went through the struggle of a broken key fob. She accidentally stepped on it with her high heels, and now the buttons stopped working. She's still able to use it, but locking it remotely is what she can't do. What I'm doing for is just finding a special type of tool to fix that key fob.

kanagavel a said...

Great Article, Your instruction solved my remote key. Thank you so much.

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John Goodwin said...

The gift that keeps on giving... I've just used the detailed information contained in your post to fix my friend's Focus alarm/remote and she was extremely happy. I'd like to offer my thanks to you on her behalf.

Many thanks,
John G

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Tim Leunig said...

"so if you don't have the two keys required to reprogram the immobiliser to accept the RFID in a new remote, swapping the battery compartment over would probably work." This worked for me - thank you :-)