The emission control light came on this morning and has stayed on. I've driven the car, left it parked up for 1 hour, started the engine again and the light is still on. Any ideas? The user manual suggests that the light staying on constantly is less urgent than if it flashes. If it flashes, the advice is to drive at a reduced speed and take to a dealer. If it stays on, the advice is simply to take to a dealer as soon as possible (doesn't say immediately). The car is a 2007 A6 3.0 TDI. I'm certain it doesn't have a DPF. I'm due to start a 250 mile journey this evening. I don't have VCDS so can't run a diagnostic. Does anyone have any ideas why this light has come on, and how risky it might be to ignore it this evening and do the journey?