1995 GMC Sierra O2 sensor locations

gommee · January 3, 2007

I have a 95 sierra 1500 4x4. I am looking for info on whether some models only have one O2 sensor just before the Catalytic converter. When changing my exhaust system, we found that there was a sensor above the flange,but it was not connected to anything. We could not find any connectors for this one O2 sensor to connect to. We removed all of the cable covers, but could not find a connector. I have a feeling that the manifold was replaced at some time using a Chevy part.

My check engine light only comes on every once in a while and then goes out. The code shows an O2 issue that I feel may be coming from the heated O2 sensor by the Catalytic. Many wiring diagrams I have found only show one, but some show 2. Is it possible that this model is only suppose to have one O2 sensor, or is there another hiding place for the connector?

SPARK CHASER · January 3, 2007

I have a 95 sierra 1500 4x4. I am looking for info on whether some models only have one O2 sensor just before the Catalytic converter. When changing my exhaust system, we found that there was a sensor above the flange,but it was not connected to anything. We could not find any connectors for this one O2 sensor to connect to. We removed all of the cable covers, but could not find a connector. I have a feeling that the manifold was replaced at some time using a Chevy part.
My check engine light only comes on every once in a while and then goes out. The code shows an O2 issue that I feel may be coming from the heated O2 sensor by the Catalytic. Many wiring diagrams I have found only show one, but some show 2. Is it possible that this model is only suppose to have one O2 sensor, or is there another hiding place for the connector?

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There should only be one sensor and it should be on the drivers side exhaust manifold

Steves95Sierra · January 3, 2007

On mine ('95 C1500 Single Exh - right-side out).., it's right in front of the Cat - just forward of the Y-connector...

gommee · January 3, 2007

On mine ('95 C1500 Single Exh - right-side out).., it's right in front of the Cat - just forward of the Y-connector...

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Is there one located just above the flange on the manifold or maybe a plugged hole?

Some wiring diagrams show 2 O2 sensors. Is it possible that this model only has 1 located before the catalytic and some one just used the one on the manifold as a plug. Like I said, there is no wiring for the top one.

Steves95Sierra · January 3, 2007

Hi gommee;

I only have the one O2 sensor (a three-wire sensor) just forward of the Cat -- nothing on the manifold. Keep in mind though, my truck is a C1500 4x2, 305 TBI (vin H), 4-spd Automatic.

We may have to appeal to Mr. GM-Tech for his wisdom on this one...

Steve. . ..

gommee · January 4, 2007

Hi gommee;

I only have the one O2 sensor (a three-wire sensor) just forward of the Cat -- nothing on the manifold. Keep in mind though, my truck is a C1500 4x2, 305 TBI (vin H), 4-spd Automatic.

We may have to appeal to Mr. GM-Tech for his wisdom on this one...

Steve. . ..

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I must appeal to Mr. GM-Tech for his wisdom on this one...

SPARK CHASER · January 4, 2007

The wiring diagrams that I have show only one sensor, but maybe the California models had two(one for each bank of cylinders)? I did find on the drawings that only 350(5.7L) engines with the 4l60e transmission are supposed to have the one wire(unheated) sensor on the drivers exhaust manifold. All others are supposed to be a three wire(heated) sensor, which are normally located on the exhaust pipes after the exhaust manifolds. What's strange about this is I have friends with trucks equipped with other engines(4.3,5.0L),transmissions and their sensor is at the same place as mine. It's like GM built these trucks with whatever parts were available that day on the assembly line.

I guess the answer to the topic starting question is: It looks like someone installed an exhaust mainfold from another truck. One that used only the one wire sensor and the sensor on that manifold is there just as a plug for the hole.

gommee · January 4, 2007

Thank you: Spark Chase and Steves95Sierra for your input and your time. You have to be correct on this, as I just put a 95 Chev and my 95 Sierra side by side. Identical in almost everything. (except O2 sensors) 95 Chev only has one (above the flange - single wire) and 95 Sierra has one connected (3 wire in front of Catalytic). I guess the previous owner of mine was lazy and did not put proper plug in hole when changing manifold.

Thank You Again...

Gommee