RS4 Warning Light Mystery: OBD Errors Persist

As someone with some experience working on cars, I had a similar issue with my 2019 RS5. The onboard diagnostics kept showing incomplete readiness monitors after a computer reset. The good news is my solution didnt cost anything. The incomplete system readiness was actually normal after the recent OBD diagnostic scan. The vehicle computer simply needed time to complete its self-tests. Here is what worked for me: Drove normally for about 100km, Included both city and highway driving, Avoided disconnecting the battery, Made sure to do several cold starts, Let the engine reach full operating temperature each time After following this driving pattern, all readiness monitors completed themselves. The vehicle inspection system needs to run through various test cycles to reset properly. Could you share: How long ago was the last OBD scan done? Are you getting any specific error codes? Have there been any recent repairs or battery disconnections? This would help determine if your situation is similar and whether you just need to complete the drive cycle or if there might be underlying issues requiring attention.

Just had my 164338km service done last month. The OBD scan was performed about 2 weeks ago, showing P0420 and P0430 codes. After checking with diagnostic tools, signs point to the exhaust system, specifically the catalytic converters showing reduced efficiency. The drive cycle method suggested is worth trying, but based on these specific codes and symptoms, the issue might be more than just incomplete readiness monitors. The warning messages started appearing more frequently during highway driving above 120km/h. Think we should also verify oxygen sensor readings before and after the cats since these codes often indicate degraded catalytic converter performance. Might need professional testing to confirm if the exhaust system components need replacement before the next emissions test.

Thanks for providing those details about the P0420/P0430 codes. You are right, my initial suggestion about driving cycles alone probably will not resolve these specific catalyst efficiency codes. After seeing similar codes on my RS5, the oxygen sensor readings confirmed worn catalytic converters. The symptoms match perfectly, increased error frequency at higher speeds is typical for failing cats. In my case, the check engine light kept returning even after completing multiple drive cycles. The emissions test showed values outside acceptable ranges. A professional diagnosis confirmed both catalytic converters had degraded beyond the acceptable threshold. Some key points from my experience: Replacing just oxygen sensors did not fix it, The OBD readiness monitors would complete but codes returned, Higher exhaust flow during acceleration made it worse, New catalytic converters ultimately resolved both codes The repair was not cheap (around 3000 Euro) but necessary to pass vehicle inspection. Given your similar codes and symptoms, I would recommend getting the exhaust system properly tested rather than trying temporary fixes. Consider checking if your car is still under emissions warranty coverage, as catalytic converters are often covered for longer periods.

Thanks for the detailed feedback on the catalyst codes. Your experience matches what I am seeing with my RS4. After trying the drive cycles for a few days, the check engine light keeps coming back, especially during highway runs. I checked the warranty situation, unfortunately my car is just past the emissions system coverage period. Looks like I will need to budget for new cats based on the repair cost you mentioned. Good to know that sensor replacement alone probably will not fix these specific codes. Will book a proper vehicle inspection with exhaust system testing to confirm the catalytic converter efficiency readings. Better to address this properly now than risk failing the emissions test or causing more damage to the car diagnostics system. Think I will also get them to check all related components while they have it up on the lift. Hoping the upstream and downstream oxygen sensors are still good, as that would help reduce the total repair cost.