I have a 4 cylinder 99 accord lx auto that has run flawlessly and has been well maintained. It's on 115K miles (mostly highway) and I just got my first dreaded check engine light. The drivability of the car is the same, and I haven't noticed any difference in the performance or gas milage (so far). I went over to Autozone and used their OBD2 scanner which read the single code, P1149. After some googling I found out that it basically means the primary O2 sensor isn't working properly. Then I found this Honda Service Bulletin on the web:

http://www.driveaccord.net/forums/at...hp?postid=5903

The bulletin says that it's a fault with the ECM/PCM (computer?) erroneously reporting a bad O2 sensor and that the ECM/PCM needs to be replaced to resolve the problem. I think the computer is a $700 part, much more expensive than an O2 sensor. Nonetheless, I wouldn't want to replace the O2 sensor if it is not going to fix the problem.

How do you guys recommend I try to figure out if it's really a bad sensor that needs replacing or if it's just the computer? If it is the sensor should I notice the gas mileage getting much worse? Or can that also happen if the computer *thinks* the sensor is bad and changes the fuel ratio. I don't want to end up having to change the ECU just to get rid of the check engine light, but I don't want to end up with lousy gas mileage either.

Any suggestions are greatly appreciated. Thanks!