CEL P0138 - Rear O2 Sensor


Ah, thanks. I see they have an NTK for $127 after shipping, but not in stock so I'm looking for other option to get it sooner.

Still not sure what the difference is between the Walker "front" and the Walker "upstream" listed on partsgeek. Different part numbers.

EDIT: Advance Auto has a code (JL28) that will knock 15% of totals of more than $100 AND you get a $50 coupon to apply on future orders of $100 or more (code works through July 28, 2012). The NTK only costs $121.54 w/free ground shipping.
 
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Finally got around to replacing the rear O2 sensor this weekend b/c inspection is due. I have to admit it took me a while to find the sensor. I am use to the downstream O2 being farther down the pipe – typically mid car. I had to Google the sensor to find the location and was surprised to see it is so close to the primary.

Working under the car on ramps, I sprayed it with Kroil and let sit for ~10 mins. Piping was still very hot and I can hear it fizzle/dissolving upon contact so not sure how much good it did; didn’t have time to wait for it to cool but I should as it was still hot on my arms. I had an O2 sensor socket (22MM, can borrow from Autozone) to break loose sensor with a ratchet + extension pipe. You can reach up to unplug the sensor with both hands. Everything came off easily. There appears to be a nice layer of anti-seize on the OE plug. The part that I did not want to waste time on and can be a nuisance is the bracket that suspensions the wiring from hot exhaust parts. The bracket is mounted to the exhaust manifold by a 10MM nut (rusted but can take off) and on top of the bracket is clamp that secures the O2 wire with a 10MM nut on a carriage bolt that has a round head -doh! This nut is also rusted + a soft metal bracket that deforms easily means you can’t easily take this off to easily to reuse. If you want to do it proper, plan some time to dermel off the nut and replace with a new nut and bolt OR get a new bracket in advance. I choose the easy way and just snip off the old wiring at the bracket, wrapped the new longer than necessary wiring around the bracket, zip tie, and be done.
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I did not disconnect the batter so it seems upon removing the old sensor and install the new, it triggered P0139 (pretty much the same thing as P0138). Rest light and no CEL for tad over 200 miles now (it would have come back by now). Nice to not have to see that red light.

I can safely assume the old sensor was done at ~30K. The wiring looks good, no loose connection, nothing visibly burnt, and the connector plug is clean as a whistle.
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Update: passed inspection and now over 300 miles and not light. yay!
 
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Any updates on this? Did you have the issue ever come back?
I replaced our rear O2 in our '10 with approx 35k when p0139 started coming up earlier this year...now pushing 47k and the codes back...may try and look around for exhaust/intake leaks or just clear the code and deal with it in the spring
 
Got P1038 today on 2nd car. Another $60 down the drain (hopefully only $25)…

1st car failed @ 31K. 2nd car failed @ 115K.


Anyone here use NTK or Kwiksen? Leaning towards the frugal (Kwiksen) since it is only downstream BUT I can only find Kwiksen for Calif non-turbo 2006-2009 2.3L Mazda3. Question for all you Cali members (if any are still around), what does this the “Cali” tag really mean? I only know of CARB = emission pain in the ass but what does Cali have to do with O2 sensor?? Is there something mechanically different that I cannot use it??
https://www.amazon.com/dp/ (commissions earned)

Rockauto: NTK 24447 (division of NGK) @ $52.79
 
After some Googling, seems Cali sepc downstream O2 is wideband, like the upstream thanks to CARB; whereas non-cali downstream is narrow band. This further perplexes the hell out me (likely supply/demand) why the downstream wide band O2 is so much cheaper than the narrow!?... ECU is programed to received certain range/values so you cannot mix. However, I saw some internet post where some say they are the same but different connector plug and you’d need to splice in and reuse the older connector but ultimately not worth the effort, IMO. $60 it is.
 
Just looked up prices for 2014MY out of curiosity. OEM parts go for $180 each from Amazon and the dealer! (wow)

I've used NGK and NTK parts before (on another vehicle). Should be good product esp. for the downstream position. I've never heard of Kwiksen.
 
Silentnoise - which O2 sensor did you wind up using? Seems I am in the same boat - inspection due by the end of the month. Any chance you have a picture of the location?
 
post 3 has link to the Walker sensor (part#) I used the past and would recommend. I just reset my CEL for now. Come inspection and I do need to replace, I will likely just go back to Walker.


Post 11 has a pic. Upstream is right in front of the CAT and downstream is right after the CAT; they are about a foot apart.
 
Current '08 GT @ 115K giving me CEL P0138.

This was the hardest O2 I've ever had to deal with in a while. With 11 years of rust and Forzda's quality, the old O2 finally came out with a piece of its mounting thread missing... It rusted on to the threading of the mounting hole. Had to torch, bang with mini sledge, apply penetrating oil, repeat a few times to get it off. The tight space (jack stands) and only able to turn 1/6ish rotation did not help. Not looking at what came out, I unknowingly put in the new O2 and proceed to destroy the threading. Later realized why it would not mount. Then needed to get 18Mx1.5 thread chase to clean out and re-thread the mounting hole and buy a thread file to re-thread the ruined new O2... Once clean, everything mounted like butter.

rcarhB1.jpg


FWIW, the NTK O2 cost a little more but a much better buy than the Walker.
NTK 24447
 
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