Audi A3 Diesel Won't Start: AdBlue System Alert

I had a similar issue with my 2015 Audi A4 diesel last winter. As someone who has some basic experience with diesel engines and emissions systems, I can relate to your situation. The symptoms were identical to what you describe. Initially thought it was just low AdBlue fluid in the tank capacity, but the workshop discovered the connection between the AdBlue tank and the SCR catalyst dosing unit was defective. The service light kept showing even after refilling the AdBlue. The repair involved: Complete diagnosis of the emission standards compliance system, Replacement of the dosing unit connection, Reset of the diesel exhaust system, System calibration Total cost was 250 Euro and took about 4 hours to complete. The car has been running perfectly since then with no warning messages. To provide more specific guidance, could you share: Current mileage on your A3? When was your last AdBlue refill? Are there any specific error codes showing? Did the issue start gradually or suddenly? Have you had any recent emission system repairs? This information would help determine if your issue is similar to what I experienced.

Thanks for the insights. My A3 has 169457 KM and had its last service 3 months ago. The dashboard alert came on suddenly during my morning commute. The workshop did add AdBlue during that service, but I never got any low fluid warnings before the car refused to start. The error codes are still pending as I need to get it scanned. Will check if the dosing unit needs replacement, since your repair experience sounds very similar to my symptoms. The service light pattern matches your description exactly.

Thanks for providing those details. My A4 had around 175000 KM when this happened, so quite similar to your situation. The sudden onset without prior warning matches my experience exactly. The injection system on these models can be sensitive to DEF fluid quality and temperature changes. After my dosing unit was replaced, the workshop explained that even with proper tank capacity, crystallization in the lines can trigger these errors. Some additional findings from my case that might help: The fuel efficiency dropped slightly before the complete failure, Scanner showed multiple SCR catalyst related codes, The system needed a full reset after repair to restore proper function The 3-month timeframe since your last service is interesting, my issue also occurred about 4 months after a routine service where they topped up the AdBlue. The workshop suggested doing shorter intervals between DEF fluid checks to prevent future issues. Worth noting the repair cost might vary depending on whether just the connection needs replacement or if the entire dosing unit is affected. Mine was 250 Euro but have heard of cases ranging from 200-600 Euro. Consider getting it checked soon, driving with emissions system faults can lead to more expensive repairs if left unaddressed.

Thanks everyone for the detailed feedback. The symptoms you described with your A4 match my situation perfectly. The workshop managed to look at my car today, and you were spot on, it was indeed the dosing unit connection that failed. They found crystallization in the lines exactly as you mentioned. The total repair came to 290 Euro including: New dosing unit connection, System cleaning, Full emissions control system reset, Fresh AdBlue fill The dashboard alert is now gone and the engine starts perfectly. The SCR catalyst and fuel efficiency readings are back to normal. Going to follow the advice about more frequent DEF fluid checks. They recommended checking every oil change rather than waiting for the tank capacity warning. Appreciate the help identifying the issue. Having your repair experience as reference helped me better understand what I was dealing with.