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Forum > Failed Smog Test > Question

1995 4.0l I6 Grand Cherokee failed NOx emissions 25 mph test. My scores are 1086 Max: 533.

I passed every other part but the NOx are too high. I replaced the catalitic convertor, it helped alot, but still failed. My next step is the O2 sensor. I was just wondering if you could point me in the right direction to passing. I have heard about changing oil, high octane fuel, complete tune-up. Would these be my best bet or do you know something I don't (i'm hoping you do). Thanks
Answer:

We think you're right with your next step... change the oxygen sensor. The CAT and oxygen sensor are the two main emission parts which control NOx production in your Grand Cherokee. High octane gas helps, but shouldn't be neccessary assuming your Jeep's emission system is working properly. posted by SmogTips Support

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