I have been seeing CEL 701 error since I got my RX8 and no one has so far managed to trace what the problem is. I have changed sparks and plugs and the MAF sensor and now I get it rarely. In fact I only get it on long trips but not in short city trips.

My next suggestion is O2 sensor but from what I've read in this forum, there are 2 sensors (front & rear). Can anyone suggest whether I should change one of them or both? If this is not too much trouble I would appreciate if someone could briefly explain what is the difference between front and rear sensor.

 

Is easy as hell to change the Rear O2 sensor.

but its a nightmare to do the front one, my hands and arms probably too fat for the job or something. so your results might vary.

I just replace the front one yesterday, I dont have a CEL or whatever. but the car seems to run better with the new sensor.

Im gonna replace the rear one as soon as I have the time(and budget) to buy it.

 

You need to find a better Mazda service department—or at the very least, a competent mechanic. A good mechanic can diagnose the problem without having to guess which part to replace; an expensive way to diagnose the problem.