Hi

My name is Richard 

I bought a 2005 mondeo st tdci a few months ago. It worked perfectly until....

In the winter the battery kept playing up(been off the road for 6 months now), it would be fine 1 day and would need a jump start the next. I was given a work vehicle and I probably drove my car 100 miles in 2 months, over a few days. So anyways, I ended up having to drive to work for a couple of weeks, it was OK for the first week, then the second week there was problem starting in the morning. I jump started it, got it to work, left it for 6 hours, got back, I tried to start and there was nothing.

The result, I thought was a dead battery, so I replaced it. After changing it, it was still doing the same thing. It wouldn't turn over, the new battery is in good condition so it couldnt be that. At this time I noticed the immobiliser light would flash continually, suggesting that the key wasn't working anymore. 

I wouldnt accept it So I thought it could be the starter motor, tried arcing the connection and the starter works perfectly, turning over the engine no problem, So it couldnt be that.

I got a mechanica to look at it, he plugged it in and looked for the key, all he could find was "low voltage errors", this was with the newest snap on computer. In the end he did his best but couldn't figure it out. Nor would he be able to reprogram a key. 

So still going with the idea of it being a key/immobiliser problem I got an auto locksmith out to reprogram the key, he did it straight away with no problems. But it still wouldn't turn over. Now the immobiliser light stays solid and after a minute it flashes 2 times then once, I looked this up and it is a fault code meaning that there is only 1 key programmed, apparently there should be 3. 

The dash lights up as it should, the starter motor relay clicks, and the starter motor works and turns over the engine from arcing the connection. The only difference is the immobiliser light. I would find it slightly convenient that an earth or something came loose specifically when the battery dies and wipes the keys. So I totally avoided that option.

I also tried leaving the ignition on, and arcing the starter, it turned over but didn't start.

So my question is, do I need to get more keys and get them programmed for it to start, or is there another issue which I am missing? 

Thanks

Any help will be massively appreciated. Richard.

It's not due to only having one key that's for certain. They key may not be being sensed properly, do the doors unlock via the fob?

Thanks for the reply.

Yes, the central locking works fine.