Audi Q7 Diesel: indicator light, black smoke and preheating light

Well, you've already done quite a few kilometers. Do you remember when the glow plugs were last replaced?

(Translated from German)

That sounds familiar. I had a very similar problem with my 2007 Audi A6. But I'm really not a mechanic, just to emphasize that. In my case, the glow plug was defective due to wear. The workshop then replaced the glow plugs, which fortunately only cost me 200 euros. But I should actually get a better picture of the situation first. How many kilometers has your Q7 already done? And how often do you drive long distances?

(Translated from German)

Hey, thanks for your answer! My Q7 already has 256871 km on it and I actually often drive longer distances. I will definitely consider your idea with the glow plugs and maybe replace them. Thanks a million for that! Do you think that could also be the reason why the pre-glow light doesn't go out? I look forward to your further assessment.

(Translated from German)

Hey, I had an identical problem with my Ford Mondeo, which had similar symptoms to yours, especially the preheating light not going out. Your theory about the pre-glow relay could well be correct, as it can happen that the relay is defective and no longer controls the pre-glow system properly. In my workshop, they first read out the OBD to check the error codes. They then identified a problem with the preheating system. The mechanics replaced the pre-glow relay and then all the problems disappeared. The replacement cost me around 100 euros, plus a few more euros for troubleshooting. However, it is also possible that your glow plugs are also defective, as WolfiJ has already said, which sounds logical to me. So, have the error codes read out and then you'll know more! Hopefully that will help you. Good luck with it and keep us up to date!

(Translated from German)

Hey, thanks for your advice! I'll definitely have the pre-glow relay checked then! And of course you're right about the error codes, first find out what's going on. In any case, thank you very much for your tips, that's really a big help!

(Translated from German)