after disconnecting the battery to try and reset the ecu the engine management light has come back on again and the car is misfiring I have put the diagnostic code reader on the car and its showing code p0335 that is crankshaft position sensor a circuit malfunction help anyone any ideas

Firstly, this appears to be the fifth thread you've created on the same issue. This will confuse. If you really want help, one thread per problem, and stay with it.

Crank sensor is mounted at the front of the engine, at the crank pulley. Easy to damage by road debris, or mishandling, especially vulnerable when changing the alternator belt. Crawl under the front and have a look. Might be easier with the RH wheel off and the wheelarch liner out the way. Fault code just reports that it is not getting the right signals. Follow the wiring up the cambelt cover, looking for any obvious damage. These have been known to fail, so a new one is probably what is needed.
http://www.eurocarparts.com/ecp/c/F...0c02296642fbd92b7b6e63b4a0111acb2d6a44&000440

One of the things I have learnt over the years of owning Italian cars is check the wiring. Check it and then check it again, clean connections, clean earths and test for continuity. Always a good place to start. Patience is a virtue on these little rascals.