Cadillac Check Engine Light Persists After Reset

Just had a similar situation with my 2016 Cadillac CT6. The check engine light came back shortly after a vehicle inspection, and the onboard diagnostics continued showing incomplete readiness monitors. This is actually normal behavior. After clearing diagnostic trouble codes, the car needs to complete several drive cycles to reset all system readiness monitors. In most cases, it takes anywhere between 50-100 miles of mixed driving (city and highway) for all monitors to complete their self-tests. For the monitors to reset properly, you need to: Drive at various speeds, Let the engine reach full operating temperature, Include some idle time, Make several complete stops My car diagnostics showed all clear after about 4 days of regular driving. If your check engine light returns after all monitors complete their cycles, then there might still be an underlying issue requiring attention. Best practice is to wait until all system readiness monitors show complete before concluding whether the original repair fixed the problem. This prevents unnecessary return trips to the repair shop.

Thanks for the detailed info about the diagnostic reset process. Same thing happened to my XT4 last month after the exhaust system repair. It took almost a week of normal driving before my onboard diagnostics showed all systems ready. Just curious, what did the shop charge you for the initial repair and computer reset? My repair bill was pretty steep at 850€ and wondering if that was typical. Have you had any warning lights pop up again since getting it fixed?

Thanks for asking about the repair costs. My situation was actually pretty straightforward. The exhaust system readings were initially causing the readiness monitors to show incomplete, but the dealer ran OBD diagnostics and found no actual hardware issues. Since the computer reset and system readiness check were performed under routine maintenance, there was no charge (0€) for that specific service. Pretty lucky there, as diagnostic fees can add up quickly with these models. The good news is that after about a week of regular driving, all monitors completed their cycles and the system readiness status has remained normal. No warning lights have returned since then, confirming there were no underlying problems. Your 850€ repair sounds reasonable if actual exhaust system components needed replacement, though costs can vary based on the specific parts involved. Just keep in mind that whenever the OBD system gets cleared, those readiness monitors will need time to complete their checks again. This is just how the computer verifies everything is working as it should.

I appreciate everyone sharing their experiences. Wanted to update that I took my XT4 back to the shop yesterday since the onboard diagnostics still showed problems after a week of driving. Turns out there was a faulty emissions sensor they missed during the first repair. The mechanic admitted they should have caught it earlier and only charged 150€ for the additional sensor replacement and drive cycle verification. Much better than the initial 850€ bill. After completing the proper repair, all system monitors finally show ready and the check engine warning is completely gone. Just shows how important it is to make sure all diagnostic tests complete properly before assuming a repair fixed everything. Glad I waited for the full drive cycle before signing off on the work.