My 2002 1.9tdi sport loses power intermittently.

it will be ok for a while then about 2500 revs it wont boost and goes into limp mode.

if i flick the ignition off and on it will clear for a short time.

the code on the computer is 17956

can anyone help?

thanks

The usual fault is where the Variable Vanes within the Turbo gum up with carbon and rather than move into position to optimise the boost, they instead stick in the one position hence the fault code and limp home. Usually caused by smoking around town and not revving engine enough to keep the Vanes from gumming up. 

Easiest (or rather cheapest) option is to run a cleaner through the turbo which should cure it...see link below

http://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR11.TRC1.A0.H0.Xturbo+cleaner.TRS0&_nkw=turbo+cleaner&_sacat=0

or the other option is to replace the cartridge section within the turbo which houses the Vanes....see link below

http://www.audiownersclub.com/parts-results/A3-S3/Turbochargers--Parts/63707

Let us know how you get on with it

Cheers   Trevor