Q7 Won't Start After AdBlue Tank Runs Empty

Had similar trouble with an A6 3.0 TDI from 2014. The service light triggered due to the SCR catalyst system, but the issue went beyond a simple AdBlue refill. The diagnostic showed a faulty connection between the tank capacity sensor and the dosing unit. The emissions control system required a complete check of the AdBlue delivery system. The main problem was a clogged dosing valve, caused by crystallized AdBlue deposits. The diesel exhaust system showed increased NOx values due to improper AdBlue injection. The repair involved: Cleaning the complete dosing system, Replacing the dosing valve unit, Verifying tank capacity sensor functionality, Resetting the diesel exhaust system This was a serious repair requiring specialized diagnostic equipment. A simple AdBlue refill would not have solved the starting problem. The SCR system needs proper function to allow engine start, as its part of the emissions control strategy. Recommendation: Get it checked professionally. These symptoms typically indicate more than just low AdBlue levels, especially with that mileage.

Thanks for sharing your experience with the A6. My Audi had a similar DEF fluid issue last winter. The injection system was completely blocked, and I also needed the dosing valve replaced. The symptoms match exactly what you described. Did you remember the total repair cost? My repair bill seemed high but wondering if it was in line with what others paid. Also curious if youve had any other issues with the emissions control system since the repair was done?

Since my last post about the A6 issues, I had the AdBlue tank output problem fixed at a certified shop. The total repair came to 250 Euro, which covered replacing the defective connection between the tank and dosing unit. The dashboard alert system hasnt shown any warnings since. The good news is the diesel exhaust system has been working flawlessly after the repair. The emissions control components are all functioning as they should, and the injection system maintains proper AdBlue flow. This is actually a reasonable cost compared to what some others paid for similar repairs. Its been about 8 months now without any new SCR catalyst issues. The repair shop did a thorough job testing the entire system after the fix, which probably helped prevent any follow-up problems. Getting it fixed properly the first time really made a difference in preventing recurring emission standards compliance problems. Based on your description, your repair sounds more extensive than mine was, so a higher cost would make sense in your case since you needed the complete dosing valve replacement.

I finally took my Q7 to get it fixed last week. You were right, it was more than just an empty AdBlue tank. The mechanic found that the injection system was completely clogged, similar to your experience. The service light had been warning me for a while, but I kept putting it off. The repair included cleaning the entire system, replacing the dosing valve, and recalibrating the tank capacity sensors. Total bill came to 780 Euro, which seemed steep at first, but after hearing others experiences, it seems fair for the work done. The dashboard alert is now clear and the fuel efficiency has actually improved slightly. The mechanic explained that a properly functioning SCR catalyst system helps the engine run more efficiently. No issues starting the car since the repair, and the diagnostic tool shows all systems working normally. Lesson learned, wont ignore those early warning signs next time. Better to address these emission control problems early before they cause bigger issues.