when one of mine went it felt like i'd thrown a piston to be honest, it was shaking and shudderingso badly i thought the worst, it was close to being undrivable and if i was further from home i would have called in the rac, but as i was only 1/2 a mile away i limped home with all the warning lights on!
.
I replaced all 4 as they were revision 'b' units and quite prone to failure (apparently) so off to
http://www.thetradepartsspecialists.co.uk/ the next day to pick up a full set for £102 inc the VAT. an hour later and the car was sweet again, no need to have any lights or fault codes cleared, just worked fine!
I worked out it was pot no. 4 and binned that one, i kept the others for future emergency repairs, one in the spare wheel well for 'real' emergencies but to be honest the RAC carry these as they break down so commonly.