Exhaust Recirculation Valve

My daughters 2002 9n Polo was bought from her cousin and one of the few "declared" faults was the engine warning light. It had been to three garages for this and the exhaust recirculation fault was the cause, but a replacement valve did not fix the problem. The assumption has been a faulty warning system, but is there another solvable cause?

I have also read that that the ECU can be reprogrammed not to recognise the EGR.

I used to drive a 1978 volvo and am only now coming to terms with modern cars. The rear screen heater wont work and I'm told the computer has lost is live output to it, but that if I was foolish enough to run a seperate feed from the battery it would detect that and totally malfunction. A £500 fix for a screen heater! Strewth.