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Discussion Starter · #1 ·
I'm getting a P0031 and P2238 CEL on my '03 3.4 MT EX-Cab Tacoma with 130K miles on it, which means my sensor's heater circuit is not working. I did some real-time diagnostics with my OBDLink MX and the sensor is still putting out a voltage reading that varies with throttle conditions, so i think it's functional as far as reading the A/F ratio in the exhaust but just not the heater portion. Some of these dealers are listing the part at obscene prices.

Do we still have any clout on here with Toyota of Dallas for parts as a sponsor? The old TRDParts4U.com site where I've ordered from in the past doesn't seem to be around anymore.

Does anyone else have a recommendation on where the best place is online to get a good price on genuine Toyota parts?

Thanks!
 

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I've purchased from sparkplugs.com. They had good pricing. Looks like you need Denso part # 234-9003 which is $158 from that site.
 

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Discussion Starter · #3 ·
I've purchased from sparkplugs.com. They had good pricing. Looks like you need Denso part # 234-9003 which is $158 from that site.
I was doing some research earlier on here about which sensor to get and 2 people reported that they had issues with the P0031 code still coming on when using that Denso sensor, and then going ahead and spending the extra money after that to get the OEM Toyota one and it made it go away. I know Denso makes the OEM Toyota parts, but I don't think that they are necessarily exactly the same as the ones you get from Toyota. Bank-2 plug wires for example are similar when branded as Denso, but not exactly the same as the OEM Toyota branded wires made by Denso for this truck. The Toyota ones are slightly thicker than the Denso wires, the Toyota ones are individually labeled with both a production date as well as plug numbers for the cylinder that they go to whereas the Denso ones are not, and the Toyota set comes with the little plastic wire holders that spaces the wires out at various points as well as the foam insulation pads at certain high-heat/high-abrasion sections of each wire.

I don't know exactly where the 2 people who tried that Denso 234-9003 sensor bought it from though....and I suppose it's possible that it was purchased from a non-reputable vendor that took a generic sensor and sold it in an OEM Toyota sensor box.
 

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Discussion Starter · #5 ·
Yeah, I did read about that. The part that sucks is you would pay twice if you try the Denso then have to go OEM.
Yeah, that's what has me nervous, and we obviously can't return an oxygen sensor either if it's been used at all. I was doing a bit more research today and read a bunch of reviews on the Denso one and it seems like most people are reporting that it works great for them. The Toyota one is nearly double the cost of the Denso branded sensor too. I decided i'll try the Denso one since it was available from Amazon.com directly for $130. If it works well i'll report back here so others will have a better feel for this in the future.
 

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Interesting... I was getting the code for Cat inefficiency with the 250K mile original sensors on my 04 Taco. I bought the Denso O2 sensors (both upstream and downstream) from SparkPlugs .com, but was still getting the code, just less often. Shortly thereafter I replaced the Cat and I installed headers. I replaced the dual cats with a 2 inch Magnaflow single Cat to have the entire exhaust 2 inch. Made no difference with how often the check engine light comes on, but it comes only rarely, usually only when I am on the trail following someone driving slow, soI just have been living with it. I just have to remember not to do any trail runs the week before smog check so as to not have the recent code. If I end up having to deal with it, I will fork out the money for OEM next time. I had been blaming still getting the code on the aftermarket single Cat verses the OEM 2 Cats.
 

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Discussion Starter · #7 ·
Interesting... I was getting the code for Cat inefficiency with the 250K mile original sensors on my 04 Taco. I bought the Denso O2 sensors (both upstream and downstream) from SparkPlugs .com, but was still getting the code, just less often. Shortly thereafter I replaced the Cat and I installed headers. I replaced the dual cats with a 2 inch Magnaflow single Cat to have the entire exhaust 2 inch. Made no difference with how often the check engine light comes on, but it comes only rarely, usually only when I am on the trail following someone driving slow, soI just have been living with it. I just have to remember not to do any trail runs the week before smog check so as to not have the recent code. If I end up having to deal with it, I will fork out the money for OEM next time. I had been blaming still getting the code on the aftermarket single Cat verses the OEM 2 Cats.
Interesting.... Which motor do you have? 5VZ 3.4 or 3RZ 2.7?
 

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Discussion Starter · #8 · (Edited)
Just an FYI followup on this thread.... I put the Denso 234-9003 sensor in my 2003 3.4 Manual Transmission 4WD Tacoma this past weekend and drove it for a few days and my check engine light has not come back on and the truck has passed all of the emissions self-readiness checks. So it looks like you don't need to get the OEM Toyota sensor and the Denso version works just fine. I got it from amazon.com directly for $130 not including tax:


That being said, it seems like my fuel economy is a little lower now with the new sensor than it was with the old one after driving it for 2 days with nothing changed except for the new sensor (going by my ScanGauge II). I have an 800 mile trip coming this weekend so I'll have a better feel for it after that, although i have also since changed my plugs and wires which could mask any minor changes in economy from just the O2 sensor.
 

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Mine is the 5VZ 3.4 as well.
 

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Good to hear the sensor worked. Any little change in sensors and closed loop operation seems to force the ECM to relearn the fuel maps. So I would expect the fuel economy to get better as time goes on.
 

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Discussion Starter · #11 ·
Good to hear the sensor worked. Any little change in sensors and closed loop operation seems to force the ECM to relearn the fuel maps. So I would expect the fuel economy to get better as time goes on.
I did clear my ECU of stored codes using an OBD-II scanner too. I'm not sure if doing that wipes the entire ECU of all persistent data including any learned maps or just wipes codes and resets the CEL to off, but hopefully my economy gets a bit better as you mentioned and maybe also with the recent list of tune-up items i performed. With the price of gas these days I kinda miss the old days of my regular cab 2.7 4x4 5-speed where I could get 25-26 MPG on a long trip by driving lightly. That same type of driving in my OEM-geared TRD 3.4 gets me about 19-21 MPG on 32's.
 

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My 2002 3.4l TRD manual trans hasn't seen 19-21 MPG since it was new, stock and on 31's. 21 MPG I might have gotten once. I would say I average 16 MPG lifted with 33's.
 
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