Hi there i"m a complete beginner at this kind of thing and so far haven't got very far.
I have worked in a garage for more years than i care to remember doing general servicing and repairs to all makes of cars/vans.
Up until a few weeks ago i was running around in a 1997 110 tdi passat that would happily do 45-50 mpg no matter how i drove it then a long term customer came in with his 2002/03 C5 2.2 hdi estate auto and said he had been offered virtually nothing for it as a trade in
so i bought it from him and started using it.
Now i wasnt expecting it to be as good on fuel as the passat but it is poor to say the least.
So after checking it out have found no real causes so decided that maybe defap'ing it and decat'ing it along with a remap may be the way forward.
First i bought a kwp2000+ which would't talk to it, then i stupidly bought a mpps type and now that will not talk to it either.
Have checked it with autodiagnos diagnostic machine which communicates no problem but will not when eobd/obd diagnostics is selected.

Is it possible for the car to run ok and talk to some equiptment but not to a flasher?
Am I right to think there is some reason the k-line signal is locked or am I way off??

Any help would be gratefully received ;) I'm willing to learn as long as it doesn't get way too techy!!

Hi,
take the ECU out of the car and do the bench.
If ECU responds than you have problem on OBD port.

If ECU still does not want to communicate than it can be more issues.

Well after leaving the car battery disconnected for about 45 mins yesterday and then installing new software for my mpps flasher today I managed to read my ecu no problems

I'm happy for you, but it is strange that it solved by removing battery. A friend of mine had the same problem and had to take out his ECU to write again with BDM

You made two things, now you can not be sure where was the problem. Always do one thing at the time, so you can isolate the problem...if you want to do good analytics you have to do systematic work.