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Trying to replace my O2 sensor on my truck and want to know which sensor to buy, I can only find one in front of the cat. So my thought is upstream. Is there a difference? Thanks.
 

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2005 Corolla CE
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Is the upstream sensor the bad one?
 

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'84 2WD Pickup
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Trying to replace my O2 sensor on my truck and want to know which sensor to buy, I can only find one in front of the cat. So my thought is upstream. Is there a difference? Thanks.
The terminology "upstream" and "downstream" usually apply to fuel injected systems. The difference between them is just the length of the cable. Since your 22R is carbureted, it only has the upstream one.
 

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Discussion Starter #5
My 91 is fuel injected but I can only find one sensor and it is in front of the cat. I don't have a carburetor.
 

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So just to update anyone who can help me. I looked up on the Denso website yesterday and found the part 234-4055. My new question is there are two different 4055's shown, one being the upstream exc California and the other being downstream California. Are they the same part since they are the same part number? I just want to order the right part so I don't waste time trying to figure things out if it doesn't work. Thanks for reaching out guys with feedback as I'm new to this.
 

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First off, I seriously doubt you have a fuel injected 22R. All 22Rs are carbureted. Are you sure you don't have a 22RE? If you're looking up parts for the wrong engine, you can't expect to get the right part.

Also, you should look at the information plate under the hood and see if yours is a California model. You'll see on the labels below that one says CAL and the other says FED.

If yours is a California 22RE and you're replacing the upstream sensor, the part number is 4056. If it's a Fed 22RE, the upstream sensor is the 4055. Yes, both listings for the 4055 are the same part. They're just calling out different applications.

If there's any question in your mind, look at the connector, the number of wires and the length of the wires.

As a side note, don't get talked into a threaded sensor with an adaptor plate. They don't always fit without modifications. The Denso models you're looking at should be a good fit.



 

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Discussion Starter #8
Many thanks my friend now I know what to look for. You are correct it is the 22re.Thanks for the quick reply. I was hoping if the part number was the same it wouldn't make a difference since it did show it was for upstream and downstream replacement.That said I'll order the part and get the replacement done.
 
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