Audi A5 AdBlue System Failure Stops Engine Cold

Had similar issues with my 2017 Audi A6 3.0 TDI. The symptoms match what happens when the AdBlue dosing unit fails to communicate with the SCR catalyst system. The fix required replacing the complete dosing module because corrosion had damaged the electrical connections and pump assembly. This is a known issue affecting diesel exhaust systems, particularly when the AdBlue crystallizes inside the unit. The emissions control system is designed to prevent engine starts if it detects SCR catalyst malfunction. This is more complex than a simple refill issue. The system needs proper diagnosis with specialized equipment to read the exact fault codes. In my case, the repair involved: Removal of the old dosing unit, Cleaning of the SCR catalyst area, Installation of updated module version, System reprogramming, Fresh AdBlue fill This was a serious repair requiring specialized knowledge of emissions control systems. The car was in the shop for 3 days. Without the fix, the vehicle would have remained in limp mode to maintain emissions standards and fuel efficiency targets. Consider having it checked at an authorized dealer who has experience with modern diesel exhaust systems.

Thanks for sharing your A6 experience. My A5 had almost identical symptoms and the dashboard alert was showing the same SCR catalyst warnings. Ended up needing the full dosing module replacement too. The service light kept coming on even after initial repairs. Did you remember roughly what you paid for the complete fix? Also curious if youve had any emission system problems since getting it repaired? The tank capacity seems fine on mine now but Im still monitoring it closely.

Thanks for the follow-up. Since getting my A6 fixed, it has been running perfectly with no further dashboard alerts related to the SCR catalyst or emissions control system. The repair cost was 250 Euro to fix a faulty connection between the AdBlue tank and dosing unit. Much simpler than initially feared. The injection system is now working correctly and AdBlue consumption has returned to normal levels. Unlike before, the tank empties at the expected rate with no leaks or dosing issues affecting the diesel exhaust components. The repair was worth every cent as it fully resolved those frustrating starting problems and warning lights. My advice would be to keep monitoring your AdBlue levels, but with a properly repaired system, you shouldnt see any more SCR-related issues.

Thanks for the advice. I finally got my A5 checked out at a different shop that specializes in diesel systems. The mechanic found crystallized DEF fluid had damaged the injection system, exactly as described. Total repair came to 1200 Euro which included replacing the dosing module, cleaning the SCR catalyst, and a fresh fill of AdBlue. Took them about 4 days because they had to order some parts. The dashboard alert lights are now completely gone and the car starts perfectly. The tank capacity sensor is working correctly too, showing proper fluid levels. Been driving for 2 weeks with no issues. Much better experience with this new mechanic who actually explained the problem and showed me the damaged parts. Definitely learned to take these emission system warnings seriously rather than just hoping a refill would fix it.