Hi Everyone.
Im in the UK. I'll get straight to it.
I have a 2008 ford mondeo titanium estate 1.8 TDI. I have taken it to several garages over the last 18 months and non of them have been able to diagnose (or even find the fault) on the car, which is as follows.
The problem:
At seeminly random points during travel (usually during motorway travel or at high speeds but not exclusivley) the car goes into limp home mode. Meaning when travelling at 70mph, the engine cuts out and will only allow me to do 15mph. When this happens, the engine malfunction warning comes on the dashboard display, and the traction control warning light comes on the dashboard.
Heres a picture of the fault
Once i pull over and let the car rest for around 15 minutes, the fault goes away and im able to resume driving. However, once the fault happens once, it keeps happening for the remainder of the journey at speeds over roughly 30-40mph. Usually forcing me to have to drive no faster than 30mph either on the motorway or dual carriage way until i can find a by-road route. which is incredibley dangerous and stressful.
Recently, i took the car to halfords (a nationwide garage chain in the UK) after getting tired of independant garages shrugging their shoulders at me, after the car faulted on a smart motorway (which for my american friends is a 4 lane freeway with nowhere to pull over at the side of the road if theres a problem apart from 100ft bays every 3 or 4 miles).
its important to note that it can go long periods of time without the car doing this, and its usually after ive been assured that it is fixed.

The "Fix's" from most recent to oldest
5 - i was told there was a fuel injector which was open circuit. The fix which was a new injector cost me £450 and i was told that it should fix the problem. However, this morning i was driving my son to school and the car went into engine malfunction, limp home mode doing 20mph around residential areas.
4 - DPF clean - After extensive googling and speak to people, it sounded like the DPF filter needed to be cleaned. All of the symptoms matched up, and my handbook said my car had a DPF filter fitted but when i got it to halfords, they said i did not have a DPF filter.
3 - Suspension check at local garage
2 - Took to same local garage for diagnostics check. No faults found.
1 - 50 point check at different garage when car was purchased to make sure it was in good working order after purchase, no faults found. Car has full service history with no faults that match on record.
Im completley at a loss. Pulling my hair out.
If anybody has any ideas on how to even begin to diagnose the fault or force the fault to happen so i can demonstrate it to a garage i would love to hear from you.

Cheers!