I got my key replicated and my car sometimes shown "Engine System Fault" before starting the engine.

Below were what I was done to start the car again:

If I move the car to different place,  the engine can start again without the message.

if I disconnect the battery, the engine can start after severl attempt.  (8-10 attempt will show "Engine System Fault")

My garage said the old focus may be affected by different mobile signal transmitter. 

If I move the car to other area, I can ignite the car again!

It's so crazy

My garage said the error code read as "Stolen car".

I don't know whether the car know my key being replicated so that it lock my car.

if anyone has the same experience and get it solve. Please share.

Every month I got this message in the open area but never happen in the indoor car park.

I feel it is very annoying.

Theft detected means that the cluster solder joints have gone down,

common MK2 Focus fault

Remove cluster and send away to have the circuit board resoldered, search ebay 

an example here for you

https://www.ebay.co.uk/itm/203374788177?hash=item2f5a14fe51:g:m0AAAOSw4tRgWhWO

Does it do same thing with both keys?  Was the new key made by cloning the old one? Or was it done the proper way - they key having a different code immobiliser chip and the ecu programmed to recognise that new key?. I don’t understand why car in open or in car park makes a difference. Mk2 focus has a common problem with soldering in the speedo console/ instrument cluster. And they also suffer from canbus communication problems between the ecu and instrument cluster in the multiple connector plugs the 2 high speed canbus wires travel through

Hit the top of your dash above your instrument cluster. If that makes the message go away or makes different warning lights come on then you probably have bad solder joints and need to get them redone.

There are videos on you tube on how to resolder  the connector pins in the instrument cluster. It’s easy to get the cluster out but there’s a lot of dismantling of the Cluster including taking the needles off the gauges to get to the correct side of the circuit board to solder it. It’s quite delicate soldering. It’s certainly not for someone to learn their first soldering attempt on but for someone with experience of soldering electronics it’s relatively easy.