Audi Q8 Warning Lights Linked to System Check Fault

As someone with some car repair experience, I encountered a similar situation with my 2021 Audi Q7 diesel. The onboard diagnostics system showed comparable error messages during a routine vehicle inspection. Since my car had just undergone an OBD2 diagnostic scan, I knew the system readiness monitors needed time to complete their self-tests. After a diagnostic scan or battery disconnect, these monitors require specific driving cycles to reset properly. The solution cost nothing and simply required: Driving for about 20-30 minutes at varying speeds, Including both city and steady-speed conditions, Making sure the fuel tank was between 25% and 75% full, Ensuring the engine was at normal operating temperature Before suggesting more specific advice, could you share: Which exact error messages are displayed? Have you recently had any work done on the vehicle? Did you disconnect the battery recently? What driving conditions occurred before the errors appeared? This information would help determine if your situation matches the typical system readiness reset pattern or if there might be underlying issues requiring professional attention. For emissions test purposes, incomplete readiness monitors can cause failures, so its worth addressing this properly.

Last service was at 85000km, now at 89728km. The drive cycle suggestion worked partially but errors came back after 2 days. After researching through technical bulletins, it seems this might be related to the diesel exhaust fluid system not properly resetting after the computer reset. The check engine light keeps returning despite completing multiple drive cycles. The error messages appear right after cold starts and usually clear temporarily once the engine warms up. Based on testing with an OBD scanner, some readiness monitors remain incomplete even after extended driving periods. Plan to have it checked at service next week to rule out any sensor issues affecting the onboard diagnostics.

Thanks for providing those additional details. Based on my Q7 experience with similar symptoms, this does sound like a more complex issue than just standard readiness monitors needing reset time. When my check engine light kept returning after multiple drive cycles, it turned out the diesel exhaust fluid (DEF) system needed a proper dealer-level reset. The onboard diagnostics were showing incomplete readiness because the DEF system sensors were sending inconsistent signals. A few key observations from my case: Cold start errors that clear up temporarily are typical of DEF system issues, Standard drive cycles alone wont fix persistent sensor communication problems, The service required specialized diagnostic equipment to properly reset the system The repair ended up involving: Full system diagnostic scan, DEF quality sensor replacement, Professional reset of the emissions control system, Verification of all readiness monitors Total cost was around 450 Euro including parts and labor. Since your symptoms match mine so closely, I recommend having the DEF system thoroughly checked when you take it in. The incomplete readiness monitors are likely a symptom rather than the root cause. Its worth mentioning to the service department that the errors persist despite multiple drive cycles, as this helps narrow down the diagnostic path.

I appreciate all the detailed feedback everyone has provided. Just wanted to give a quick update after taking the Q8 to service today. The diagnosis confirmed the DEF system issues that were suggested here. The onboard diagnostics showed exactly what was discussed, faulty signals from the DEF quality sensors affecting the overall system readiness. They performed a complete exhaust system diagnostic scan which revealed two failing sensors. The repair included: Replacement of DEF quality sensors, Full system reset with their professional diagnostic tools, Verification of proper emissions system operation, Complete drive cycle to confirm all readiness monitors Total came to 520 Euro with parts and labor. The check engine light has stayed off and all readiness monitors are now showing complete after a proper drive cycle. This matches what others experienced with similar symptoms. Thanks for helping me understand the likely cause before the service visit. It made discussing the issue with the technicians much more productive.