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Old 05-16-2018, 10:12 PM   #166 (permalink)
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Originally Posted by California98Civic View Post
So if that is the code, then your upstream (top) o2 sensor is not heating quickly enough or properly. If that is the code and the failure, then your MPGs should drop and badly because that is the sensor that feeds data for the ECU to set AFR. Without good, quick data and good heating, the AFR will run rich, probably in open loop. So if this is the proper code, then I think you have a mild--even intermittent--O2 failure, which is a prime candidate for cleaning the O2 and saving some bucks. Clear the code to shut of the CEL after you double check which one it is and record it. I would not be surprised if it does not come back right away. Then clean both sensors. That's my thoughts.
How bad would they be? Would it be possible for it to go bad and still get these MPGs by hypermiling, but get even better after replacing/cleaning?

RPMs are consistently dropping out of "warm up mode" at an engine coolant temp of 71C.

Would it be possible for something to throw the error without it existing? I reset it a while back and it returned about 5-10 seconds after starting my car.

EDIT: and is it possible to ruin the O2 sensor by cleaning it?
2006 New Formula Red Honda Insight MT, 267k: (Build thread)

Last edited by mpg_numbers_guy; 05-16-2018 at 10:18 PM..
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