As with all the VAG (Volkswagen Audi Group) car's Audi may have Ignition coil problems, engine will run rough and lack performance, engine management light will be on, without test equipment the only way to find out which coil is at fault is to substitute a new coil, until the faulty unit is found and the engine runs smoothly, if the warning light doesn't go out try turning ignition on and off 6 times. See misfire.
If the DPF light is the only warning light on, you should drive vehicle at over 2000 rpm (to raise exhaust temperature) for 20 minutes without delay, this should regenerate the particulate filter (burn off the accumulated soot) and the light should go out.
If you have DPF light and the engine management light are on together, have vehicle towed to dealer. The dealer will be able to make the vehicle, with the aid of diagnostic equipment go into forced regeneration and clear filter.
Don’t run vehicles with diesel particulate filters on 100% bio-diesel only use EN 590. Only use low ash engine oil (VW 507 00).
Brake light switches can be a problem, it has two switches in one, half puts the stop lights on, the other tells the computer that you are applying the brakes, so it can turn off the fuel injectors, if the engine is coasting, saving fuel and cutting emissions. The engine management light or EPC (Electronic Protection Control) will be on sometimes and the engine will run normal.
If a Felca cuts out and won't start, check fuses if blown check wiring loom for chaffing under bonnet on the ECU computer mounting bracket, repair, insulate with tape and re-route loom.