exhaust overheat light on
 

Sorry to post this question here as it belongs in the ecu section, but I wasn't getting any responses there...

I just got a used PFC from a fellow forum member. After installing everything and reseting the PFC the exhaust overheat light is on. I checked the monitor sensors section and the voltage of the O2 sensor is a little irratice switching between .01 and .03.

I previously had the check engine light on and ran the codes which indicated I needed a new O2 sensor. I had the O2 sensor replaced about 500 miles ago. The check engine light began appearing again saying the O2 sensor was messed up again. I ignored this because I had just replaced it and I trusted the mechanic who did it as he has done all the difficult jobs (stuff I can't do) on my RX7 flawlessly.

Is there any explanation for this?
Is it normal for the light to illuminate upon putting the key in the on position - I haven't started the car with the ecu yet?

From what I've read in the searches I've done there is no clear concensus... Any input is appreciated.

Thanks
Jason

a flat o2 sensor output will trip a code. it may be an open in the wiring or poor connection to the new o2 sensor. you can also turn off the o2 feedback in the pfc