Hi

Hi I have an 04 plate MG ZS 120 and My Engine light keeps coming on. When I plug the code reader in it comes up with two faults. The first one it lists is just N/A (what does that mean?) and the second one is P0443 which is pge valve circuit. I have also noticed that before every time I start the car and go driving, if I unscrew the petrol cap and put it back on then the light wont come on. There is no problems with the the running of the engine, it goes really well. I have taken it to the garage two or three times now and they cant seem to find a problem. I have replaced the purge valve from an 03 plate 45 in the scrappy. I have sprayed everything in WD40 to make sure water is not getting anywhere and I have replaced the fuel cap as someone said it cound be that. The light always keeps coming on!!! Am I doing any damge? what does the N/A code mean? and how do I sort out the purge valve or purge valve circuit? Can anybody help me?

Thanks in advance. Graham