VW Touareg Won't Start: DEF System Failure Alert

Similar issue occurred on my 2016 VW Tiguan diesel last winter. Being somewhat familiar with diesel engines and emission systems, I initially thought it was just low AdBlue fluid too. After checking the error codes related to the SCR system, the workshop discovered the AdBlue dosing unit connection was defective. The service light kept coming on even after refilling the tank, which was the key indicator that there was more to it than just empty fluid. The repair involved: Complete diagnostic scan, Testing the AdBlue supply line, Replacing the connection between tank and dosing unit, Resetting the emission control system Total cost was 250€ for parts and labor. The dashboard alert disappeared after the repair and the car has been running perfectly since then. To better assist with your situation, could you share: Current mileage? Full error codes showing up? Whether the service light remains on after filling AdBlue? Any unusual exhaust smells or excessive smoke? Previous SCR system repairs or maintenance? This would help determine if your issue matches what I experienced or if its something different in the emissions control system.

Just had my last service at 78050km and they checked the SCR catalyst system thoroughly. My experience actually turned out different from yours. The error codes initially pointed to the SCR system, but even with a full DEF fluid tank, the problem persisted. In my case, it was actually a faulty wiring harness connection near the tank sensor causing false readings. The tank capacity monitor was showing correct levels but sending incorrect signals to the emission standards control unit. The repair cost was higher at 450€ since they had to partially remove the tank to access the wiring. The fuel efficiency dropped noticeably before the fault appeared, which was apparently an early warning sign I missed. Worth checking if you noticed any similar symptoms.

Thanks for the feedback on your repair experience. My Tiguan also showed similar deceptive symptoms where sensor readings appeared normal despite the underlying issue. Looking back, I also noticed reduced fuel efficiency about two weeks before the complete failure, dropping from the usual 7.5L/100km to nearly 9L/100km on highway drives. The wiring harness issue you described is particularly interesting because it matches a known weak point in these VW diesel emission control systems. While my dosing unit connection was the culprit, the entire SCR system design makes it prone to electrical faults that can mimic other problems. My workshop also mentioned they've seen several cases where the injection system shows similar error codes but from different root causes. The complex integration between the SCR catalyst and various sensors means diagnostic codes alone aren't always reliable indicators. Since your repair involved higher costs due to tank removal, did they mention any preventive measures to protect the new wiring from similar issues? With my repair, they applied additional protective coating on the connections to prevent future corrosion in the emissions control components.

Thanks for all the useful details about the DEF fluid and wiring issues. After getting everything fixed and monitoring the dashboard alerts for several weeks now, I can confirm the fuel efficiency is back to normal. The injection system seems to be working perfectly, maintaining a steady 7.5L/100km on the highway. The workshop actually installed a protective cover around the new wiring harness to prevent moisture damage. They said this should help avoid similar issues with the tank capacity sensors in the future. The diesel exhaust system is running much cleaner too, no more strange smells or performance issues. For the cost difference, turns out my higher repair bill of 450€ included a full system diagnostic and replacement of some worn SCR catalyst components they found during the tank removal. While expensive, it probably saved me from future emission standards compliance problems. Still keeping an eye on the service light just in case, but so far everything is working as it should. The experience taught me to pay more attention to fuel efficiency changes as early warning signs of potential emission control system issues.