Audi A6 Diesel Start Failure Despite Full DEF Tank

Had similar issues with a 2015 Audi A3 2.0 TDI. The service light came on followed by complete shutdown due to DEF system malfunction. The tank capacity showed normal but the injection system was not receiving the fluid properly. The root cause was a failed dosing unit, which blocked proper DEF flow to meet emission standards. The dosing module had corrosion build-up, preventing proper communication between the tank and injection points. This is a known issue that affects fuel efficiency and can trigger complete system shutdown. The fix required replacing the complete dosing unit and cleaning the DEF lines. While not catastrophically expensive, this is considered a serious repair as it affects the entire exhaust after-treatment system. Without repair, the car will eventually refuse to start as a protective measure. Worth noting the error codes need proper diagnostic equipment to identify if its truly the dosing unit or just sensor issues. Best to get it checked soon as continued operation could damage other components in the emission control system. This type of repair typically needs specialized tools and expertise with diesel exhaust systems. Parts availability can affect repair time.

Thanks for sharing your experience. Your symptoms match what happened to my A6 last winter. Several dashboard alerts appeared before it refused to start. The DEF fluid and injection system issues were similar too. Just wondering, what was the final cost for your repair? Also, has the fix held up well since then or have you noticed any other emission-related problems? In my case, the fuel efficiency dropped noticeably before things went completely wrong, but I ignored the early warning signs. Wish I had acted sooner.

After seeing a certified mechanic, the AdBlue system issue was fully resolved. The fault was traced to a defective connection between the tank and the dosing unit, which prevented proper DEF fluid flow needed for emissions control. The total repair cost came to 250 Euro, which included diagnosing and fixing the faulty output line. Since the repair, the diesel exhaust system has functioned perfectly with no further emission-related problems. Fuel efficiency returned to normal levels once the DEF injection system was working correctly again. The repair has proven reliable over the past months, with all emission standards being met and no warning lights reappearing. Getting it fixed promptly helped prevent more extensive damage to the exhaust after-treatment components. The tank capacity and dosing are now working as designed, maintaining proper emissions control. The lesson learned was that addressing DEF system faults early can prevent more costly repairs and potential damage to other exhaust components down the line.

I finally took my car to a certified Audi specialist last week. They diagnosed a faulty DEF fluid dosing module and damaged SCR catalyst. The dashboard alert had been warning me for weeks before the car refused to start completely. The repair cost totaled 780 Euro including parts and labor. They had to replace both the dosing unit and clean out the entire DEF injection system. The mechanic showed me the corroded parts and explained how the blocked lines had affected the diesel exhaust system. The service took two days since they needed to order specific parts. But the results were worth it, no more service light warnings and the engine runs much smoother now. Fuel consumption has improved noticeably too. Looking back, I should have reacted faster when the first warning signs appeared. At least now I know what to watch for and where to go if similar issues come up again. The specialist really knew their stuff with diesel emission systems.