Key fob programming (or not)

[PaulGover]

I guess it's worth sharing my experiences, which might help someone in future.

The buttons on my keyfob stopped working. A new battery didn't fix the problem. While fitting it, I noticed a nasty goo leaking from one of the small components on the circuit board, so I surmised it was dead, and got a new transmitter. That didn't fix the problem. I tried the instructions in the handbook, to hold the headlights on while switching the ignition to position 1, and then flashing the headlights 5 times.
It didn't work; as it didn't get the chimes or flashing security light, it seems the initial part of the process wasn't working.

My FoxWell ODB-2 scanner claims to be able to reprogram the car's ECUs for new transmitters (and transponders, but (a) that wasn't needed, and (b) if it goes wrong, it bricks the car!). It warned me it would delete the old transmitter details and then add the new ones. It did the first part OK (my wife's keyfob stopped working), but not the second. So, no remote unlocking; using the key in the door and ignition still worked.

I checked the ECU in the driver's door - all fine, and looking at its placement, it's very unlikely to ever suffer from dirty contacts, water damage or any other issues often claimed to be the cause. It's just a nice circuit board in a plastic box with decent connectors.

Some instructions on the web tell you to hold your keys near the rear-view mirror to be near the aerial. That's rubbish - the aerial is in the ECU in the driver's door, so the hold the keyfob by the handrest. Didn't help though.

I took the car to the dealers (for MOT and Service too), and they did succeed in programming one key. The important fact here was they noticed both batteries were flat, and replacing one battery from their stock fixed the key. They didn't have a second battery, so they couldn't fix the other.

Now you'll remember I'd replaced one battery with new already. So I wonder if there's a difference in battery suppliers, or possibly I used the wrong sort of battery (lithium or alkaline or whatever) technology that causes these problems.

For anyone who hasn't had to take a key apart, there are two major components: the metal key and the plastic bit holding it, which forms the top half of the fob, and the push-button part holding the battery and circuit board which forms the lower part. They are entirely independent.

The part with the key is referred to in the literature as the "transponder", and itself contains some circuitry that operates when you put the key in the ignition switch; that shares a code with the car's ECUs to enable the engine to run. The metal key can operate the door and boot locks, but using it there doesn't interact with the ECU's, hence if you open a door using the key, the alarm system starts chiming and you have to insert the key in the ignition to turn the alarm mechanism off before it starts blaring the horn.

The push-button part is entirely separate, and contains a transmitter that interacts with the security system to unlock the doors etc.

[3.8etypephil]

Did you do exactly as outlined @?

https://jagchat.net/thread/2723/x350-x3 ... ming-guide

I have found than Energiser branded batteries do not always work in these fobs. Duracell brand have yet to give me any problems.