Hello, I have a 2001 Honda Accord, 2.3L, 4 cyl, LX, 260,000 miles. It is running great, and if not for the check engine light I would not have thought there was an issue with it.

The P1166 and P1167 codes point to the o2 sensors, and I have already replaced both the upstream and downstream o2 sensors in hopes that would fix the CE light, but each time I clear the codes, when I start the engine again the CE light comes back on instantly, without any driving and without the engine idling for any amount of time at all. I was told by one person that this means it is a "hard code", since the CE light comes back on before the engine even has time to calculate any values of the running conditions (such as the fuel/air ratio at the o2 sensors, etc)...and the recommendation I got was to send the ECU in for testing since it may be a bad ECU.

I'm really hoping to avoid that, partly because of the cost, but also because I can't be without a car during that time. Again, the car runs great, so I have been continuing to drive it for the past week or so while I'm trying to diagnose it.

I was also told it could be a vacuum leak or a bad MAP sensor, but I could not find a vacuum leak, and after putting in a new MAP sensor and clearing the codes, the CE light came back on instantly the moment I started the engine. I also cleaned out the throttle bore about a month or two ago, so that should still be pretty clean (that was another suggestion I got).

I would greatly appreciate any suggestions for other things I could check or repair to possibly solve this issue!