Redpit10

Ok so I just have a basic question that I could not answer with search. I want to replace my rear O2 sensor. From my searching I have learned that it is a 4 wire, correct? I've had mine out numerous times, but I can't remember if it was a 3 wire or 4 wire. Stock Mazda O2 sensors are pricey and im not sure if replacing the O2 sensor will fix my problem, so im hesitant to pony up the cash. So will a generic four wire O2 sensor spliced into our stock harness do the trick or do I have have to bite the bullet and buy the part from mazda. Anybody know for sure?

Razz1

I know Daddy Rat Fink can answer this one and Mazda Maniac

dannobre

iTrader: (3)

There are 2 O2 sensors...front is a current based WB...and the rear a more normal narrow band sensor. The rear could probably be retrofitted with a 4wire Bosch sensor...but the Mazda one isn't that out of line in price compared to generic if you figure in the wiring and pissing around

The wideband one in the front is not likely to be available yet aftermarket...so you are likely stuck with an OEM replacement for it....

The PCM will likely throw very specific codes for an O2 sensor failure and there are Monitoring routines that monitor the efficiency of them...so if the code isn't there...it is likely OK. O2 sensors and CAT's are very tightly controlled by emissions regulations...and the OBDII crap does a good job of monitoring that kind of stuff

If you don't know if it's the problem...maybe borrow one from a buddies car if it the front one

DarkBrew

My rear O2 sensor caused a P0037 CEL
I bought OEM Mazda part on Ebay for $82

Redpit10

Dan

I know the rear O2 sensor is what is causing the CEL, but im unsure if changing it will resolve it. Honestly I've only seen about 3 8's up here in the past year, so borrowing one isn't an option for me. It would be nice though. I have a high flow cat and am getting the too lean code. My dealer even took a look at it, and said they tried their best to allow my O2 sensor some wiggle room before throwing a CEL (most likely BS). But he also told me that I will probably fly through O2 sensors if I keep the high flow cat. My dealership is great and I do trust them somewhat (they even commented that I had the best sounding 8 they've ever worked on, and that he would not chnage a thing and just deal with the CEL). What do you think. New O2 sensor solves the problem or puts me right back where Im at now? The car ran fine (no cels) for the first 6 months.


Also lately the CEL comes and goes, so I feel it could be faulty. Would it throw a different code for a faulty O2 sensor?

DarkBrew

http://smrmicro.com/rx8servicemanual/
Diagnostic codes, chapter 4 starting around page 3

mazdatech177

if its the p2096 code that i think you are talking about then there are a couple of possibilities here. i believe the definition of the code is something like "shrtft12 too lean" or something like that.. the pcm monitors your downstream o2 sensor to determine catalyst efficiency, well as your cat ages it will drop in efficiency, the pcm will see that via the downstream o2 senor input. as eff. drops the pcm alters fuel delivery to compensate for the aging cat. my first step would be to install stock cat and drive it. if you have access to a device that lets you monitor the downstream o2 sensor then hook it up and watch it. if at steady vehicle speed and even steady throttle you see the o2 sensor voltage input dip low for a bit then come back up to the 0.7-.9v range then replace the o2 sensor(warmed up cat and 02 sensor should have a steady output of the above range with little or no fluctuation). if no dips are noted and you still have a cel then its probably time for another engine. ive had several cars with that downstream o2 lean code and only one has been an o2 sensor problem.. the others required a new engine to fix. the first one of these i saw was one of the first mazda had to deal with as well, we went around and around replacing parts.. coverters, o2's, pcm flashes, air pumps. in the end they told me to replace the engine and the car never came back after that for that problem.

to summarize, put the stock cat back on and drive it after clearing the code to see if it returns. if it does, try a new mazda o2 sensor, if you still have a problem, youll probably need an engine

Redpit10

OK so I just bought a scangauge 2 so I will be able to pull the exact codes and monitor the O2 sensor. I should be getting in a week or so. I will post my results then. Thanks for the help and most likely the future help in a week.

DarkBrew

Good choice.

Redpit10

Yeah it seems like a great deal. I was going to spend $80 on a code reader and this does so much more for less than double the price.

swoope

iTrader: (5)

if it is the 171 code i might have some insight for you. how many miles???


beers

Redpit10

I have 37,000 miles on the car.

Redpit10

OK so I got my scan gauge (the gauge is awesome by the way Dark) and pulled the codes. It turns out I had two codes, but to be honest I am running with an O2 bung (I know, I know. They don't work, but I had one laying around so I gave it a shot). The codes that got pulled were P0139 and the dreaded (da dun daa) P2096 that Mazdatech was speaking of, but I'm not worried yet as the bung would throw off O2 readings very significantly. I'm going to start my code search now, but any additional info or advice would be appreciated. Thanks.

DarkBrew

Glad you like the gauge. In the Scan Gauge II review thread there's some X gauge code to enter.

Back to the codes
http://sci-fi.ptenthusiasts.net/photo4.html

There's even pictures in this one
P0139 O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)
P2096 Down Stream Fuel System 1/2 Lean

Everything is related to the sensor.

Redpit10

Well, I just finished putting on the stock cat, so time will tell whether its the O2 sensor or the cat. Only pain in the *** was getting the turboXS exhaust to meet up with stock cat, but I just used both donut gaskets on top of each other (stock one and turboXS one and they seal very well for the time being). Thanks everybody ill keep you posted and i'll check out the scan gauge thread too.

swoope

iTrader: (5)

https://www.rx8club.com/series-i-tech-garage-22/rx-8-technical-info-cel-codes-pcm-pin-list-collision-guide-26291/

sensor codes are here..

beers

sid8406

I'm getting the p2096 right now also. I'm around 28000 miles and i put a new exhaust certified by mazda speed on my Rx8. My question is, is it as simple as an oxygen sensor is may it be just the back pressure froming in the exhaust or what. I still have the stock catylytic convertor installed all that change was back of the convertor. The warning only comes on once in a while. Is this something I need to worry about or just soemthing I can over look?

DarkBrew

Welcome to the forum. I don't think that you should ignore any CEL without understanding why it's happening.
The cat back system should not have any impact on upstream parts. Perhaps they damaged some wires while installing the exhaust..?

sid8406

I plan on putting it up on a lift and taking a look underneath to see if i did damage something or if I'm sucking air or maybe a leak so thanks for the advice. For anyone still following this i did contact mazda about ti and i'm waiting for a reply to see what they say. I'll post whatever they tell me as soon as I get it.

Redpit10

Well, it was my high flow cat causing the problems. I have over 200 miles on the car since I changed to my stock cat and my car is running perfect. No cels or issues. I spoke to Ari at Rotary Performance and he said to ship the cat back and he will cut out the old cat and replace it with a new one. Great customer service there. Thanks for all the help.

-Nick

pilotedge

I am very glad I found this thread. I am in the UK and my RX8 just failed an MOT after I spent 6 weeks taking the sill and floorpan back to bare metal and treating/respraying ready for winter.
#It failed on CO levels, the thing is varying between .3% and 1.1% quickly and the limit is .2%

No CEL light but the O2 sensor voltage is all over the place. .7v for a few seconds then down to 0.1v and back up.

I have ordered a 4 wire denso sensor and it should arrive tomorrow so I will vut off my plug wire it on and see how we fare.

I hope others in the UK failing MOTs can find this thread.

UK Mazda RX8 MOT fail emissions

puppet623

iTrader: (1)

Well atleast it fixed urproblem ur bump was worth it it lol

HexRX

Eh I got the p2096 & p0139 codes after installing my midpipe and o2 bung (I know it was free though).
I can't figure out though if the p2096 is caused by the mid pipe though

pilotedge

My new lambda sensor came today, I soldered it onto the original multiplug and fired up the engine. The emissions cycle hasn't completed yet on the ODBII but it is running nicely and passed an emissions test. 0.17% CO.