hi im a mechanic working for an independant garage and just had a A8 3.0tdi quattro with only 40k on the clock and will not start the code 16725 camshaft signal implausible is logged. the customer had taken it to some audi specialist who said there is a problem with the cam timing due to a chain problem.On recieving the vehicle and chatting to customer ascertained that the cam sensor had been changed and wiring checked. Knowing what goes on in certain workshops i decided to recheck the wiring and when i saw that the tamperproof metal bracket on the ecu had not been removed i knew it was unlikely the wiring had been checked properly.i found no problem with the wiring and decided to remove the engine to check the cam timing.Working alone with no workshop manuals at hand and no experience on this vehicle or engine but still managed to remove the engine,gearbox,cradle,driveshafts,hubs and wiring as a unit in 6 hours. Finally got to the nitty gritty after removing both rear cam covers and saw that the left hand bank chain guide had broken causing the chain to be slack and advancing the timing on that cam.(the tensioner and guide are one unit) thats as far as i have got with it so far and now have to remove the gearbox,flywheel and rear timing chain cover to check for foriegn objects and if any other parts of the chain drive has been damaged before i price up the parts at audi.I am surprised to see this sort of problem on a vehicle with such low mileage The question i would like to ask is this a common problem with this engine? Do other Audi chain driven engines have this problem?