Can I use downstream o2's as my upstream ?

Contour Enthusiasts Group Archives

I'm going to order some new oxygen sensors for a tuneup.

The circular ones are listed as the rear (or downstream ?) sensors for the cats and the square connectors are the upstream ones for a/f, right ? Thing is, the o2 connectors on my contour for the upstream o2's are circular than square. Yes. Ford, built on a Friday.

Now, if I order the downstream ones (Denso PN: 234-4609) will this hurt my car ? Are the sensors themselves different or are they all the same ?

Thanks.

UP stream (closest to the engine) is square and down stream (after the cats) is round. The sensor is the same, but the plug and wire lengths are different. If you change the plug you should solder and shrink tube the new one. Don't use the solder less butt connectors otherwise you're likly to run into problems down the road.

Where did you hear that the sensors are the same? It is my understanding that they are NOT the same, and will provide problems if anyone does this EXACT thing (previous threads are all because someone just "ordered 4 sensors and they are the same")

Please indicate how/where/anything you say they are the same.

Originally posted by Ray:
Where did you hear that the sensors are the same? It is my understanding that they are NOT the same, and will provide problems if anyone does this EXACT thing (previous threads are all because someone just "ordered 4 sensors and they are the same")

Please indicate how/where/anything you say they are the same.

Ray, so it's a big *NONO* to order downstream (circular) oxygen sensors as my upstream ?

How come the universals for the front and rear have the same PN when ordering from sparkplugs.com ?

So what's the solution ? Order universals and splice or just use the downstream o2's in the upstream ?

I'm confused.

I,d like to know also!The downstream o2 sensor on the
mustangs have the same connector.I wonder if I could
use the mustang o2 sensors?

Originally posted by Ray:
Where did you hear that the sensors are the same? It is my understanding that they are NOT the same, and will provide problems if anyone does this EXACT thing (previous threads are all because someone just "ordered 4 sensors and they are the same")

Please indicate how/where/anything you say they are the same.

In most cars they are the same. What usually will make them a different "exact fit" part # is plug design and wire length. Usually the universal design will have the same part # for up and downstream just as ODC stated. In some cars they are physically different, but for the Contours/Mystiques the sensor its self (not counting the wire length and plug design) is the same. There is no reason why anyone should have trouble with converting an upstream sensor to a downstream sensor unless they splice the wires incorrectly. I've been soing it for years and on hundreds of cars and have never had one single problem.

No! Not only are they physically different sizes (the probe that goes into the exhaust) but the connectors are different. Not only that but the "rear o2s" aren't even that. They are what Ford calls a "catalyst monitor". They both measure the amount of oxygen, but the HO2S1s operate on a broad range from about 100mv to 900mv and switch constantly having many cross counts. The Catalyst Monitor or HO2S2 operate between 300-400 MV and do NOT switch much. Even if you were able to splice the wires and "make it work" and it functioned correctly, the longivity of the sensor would be reduced. There is a reason why Ford spent the time engineering 2 different sensors. Seriously just get the right sensor...

Mike

Originally posted by giddyup306:
No! Not only are they physically different sizes (the probe that goes into the exhaust) but the connectors are different. Not only that but the "rear o2s" aren't even that. They are what Ford calls a "catalyst monitor". They both measure the amount of oxygen, but the HO2S1s operate on a broad range from about 100mv to 900mv and switch constantly having many cross counts. The Catalyst Monitor or HO2S2 operate between 300-400 MV and do NOT switch much. Even if you were able to splice the wires and "make it work" and it functioned correctly, the longivity of the sensor would be reduced. There is a reason why Ford spent the time engineering 2 different sensors. Seriously just get the right sensor...

Mike

So misguided......

At the very least then, how do you explain the same universal part # for upstream and downstream?

They serve a different function, but they are the same sensor. Go with what you feel more comfortable with though.

Originally posted by Figols:

Originally posted by giddyup306:
No! Not only are they physically different sizes (the probe that goes into the exhaust) but the connectors are different. Not only that but the "rear o2s" aren't even that. They are what Ford calls a "catalyst monitor". They both measure the amount of oxygen, but the HO2S1s operate on a broad range from about 100mv to 900mv and switch constantly having many cross counts. The Catalyst Monitor or HO2S2 operate between 300-400 MV and do NOT switch much. Even if you were able to splice the wires and "make it work" and it functioned correctly, the longivity of the sensor would be reduced. There is a reason why Ford spent the time engineering 2 different sensors. Seriously just get the right sensor...

Mike

So misguided......

At the very least then, how do you explain the same universal part # for upstream and downstream?

They serve a different function, but they are the same sensor. Go with what you feel more comfortable with though.

i'm with figols on this one, the last time i did my o2's they were all universals,all with the same part#,same box,identical,only thing different was the harness plug i used (square or round)never had a problem with my sensors

For what it's worth, just because some of the aftermarket providors use the same part number for both doesn't mean that is the best answer. There is often an gap between the correct part and a part that can "get by".