Failed OBD Test After Repair? Quick Reset Guide Here

I had a similar issue with my 2005 Chevy Malibu last month after replacing the oxygen sensor. The OBD readiness monitors weren't set, causing the same symptoms you're describing. The drive cycle needs to be completed to reset all monitors. For me, it took about 3-4 days of normal driving (roughly 100 miles) before all systems were ready. The process includes: Starting with a cold engine, Highway driving for 10-15 minutes, City driving with several stops, Idling periods Your symptoms suggest incomplete drive cycle rather than a serious issue. The stored fault code should be cleared using a scanner first. If monitors don't set after a complete drive cycle, there might be an underlying problem requiring diagnostics. Taking it back to the original mechanic makes sense since they're familiar with the recent work. Make sure they verify all sensors are properly connected after their repair work. Remember that vehicle inspection requirements need all readiness monitors to be set except for two on pre-2001 vehicles, or one for 2001 and newer.

Thanks for sharing your Malibu experience, that's really helpful info about the drive cycle process. My check engine light ended up being related to a loose gas cap of all things, but I had similar readiness monitor issues too. Have the readiness monitors finally set on yours? Just curious if you remember what the repair cost was for the oxygen sensor swap, and if any other emissions test related problems popped up afterward? I'm trying to get a sense of typical costs since I might be looking at similar work. This drive cycle stuff can be pretty frustrating when you're trying to pass vehicle inspection. Mine took almost a week of driving before all systems were ready. The exhaust system seemed especially picky about completing its tests.

Good news, everything's sorted with my Malibu now. The readiness monitors all set properly after completing those drive cycles. Actually got pretty lucky with the oxygen sensor fix since the mechanic did the computer reset and diagnostics check as a courtesy, no charge. The sensor replacement itself was covered under my extended warranty. The key was being patient with the drive cycle process. Once I stopped obsessively checking the onboard diagnostics and just drove normally for about 4 days, all systems passed the readiness check. The car diagnostics showed everything working properly after that. Haven't had any emissions-related issues since the repair. Just make sure your car gets a good mix of highway and city driving during the reset period. The vehicle inspection monitor status will update itself, no need to keep checking it constantly like I did at first. Funny how we both dealt with similar problems. These readiness monitors can be finicky, but they usually sort themselves out if you give them enough normal driving time to complete their checks.

Thanks everyone, wanted to share how this got resolved in case others run into the same thing. Finally took the car to a different shop since the first mechanic seemed stumped. The new mechanic found that during the initial repair, a connector to the exhaust system sensor wasn't fully seated. That's why the onboard diagnostics kept failing the readiness tests. Cost me €85 for the diagnostic check but at least they found the actual problem. Had to do the full drive cycle routine, lots of mixed driving over about 5 days before the computer reset fully completed. The system readiness monitors finally all passed. Such a relief when that last one cleared right before my inspection was due. Lesson learned, sometimes it's worth getting a second opinion when things don't seem right after repairs. Really glad I didn't just keep driving it hoping the monitors would magically reset themselves. Having someone who knows diagnostics make that small fix saved me a lot of headache.