I was researching for the rear 02 sensor replacement on my 1994 Mercedes E320 wagon. I came across this universal 02 sensor as describe on ebay: https://www.ebay.com/itm/New-O2-02-Oxygen-Sensor-Universal-4-Wires-For-Lexus-Acura-Honda-Isuzu-GMC-SG450/261706342710?fits=Year%3A1994%7CModel%3AE320%7CSubmodel%3ABase%7CEngine+-+Liter_Display%3A3.2L%7CMake%3AMercedes-Benz%7CTrim%3ABase+Wagon+4-Door%7CEngine%3A3.2L+3199CC+l6+GAS+DOHC+Naturally+Aspirated&hash=item3ceee9e136:g:nF4AAMXQMTlRb4u2#vi-ilComp

There are four wires on the 02 sensor (see picture on ebay) One black, one gray, and two white wires. When I looked at my old 02 sensor, it has the same color types as the universal 02 sensor. My question is the two whites wires on both the 02 sensors are both the same and does not matter which white wire connected to the rest of the wiring of 02 sensor on my Mercedes as long as the matching color is white? Any comments, feedback/advice is greatly appreciated.

The white wires should be for the sensor heater but check with an ohm meter. Polarity won't matter.

X2 on check the old one with an ohm meter first or try to find a wiring diagram/instruction page. Also X2 on white wires for heater, polarity should not matter.

NGK and Bosch universals are not much more costly, I'm not familiar with that brand.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

97 SL320 and Sugar Bear, thanks for your last posts. I appreciated it. However, I am trying to remove the last remaining black connector on the downstream 02 sensor. The black connector will twist and turn and not coming out. Is there some push tab in there to remove the black connector from the other green connector? How to remove this black connector without damage the other end of the green connector? See the 2 pictures. Any Ideas?

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It looks like the female end of the black connector has grooves in the sides. I'd try taking a small screwdriver and pry those grooved ears/tabs back. You could just cut and splice the wire if needed but i'd try to reuse the connector as you are.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Thanks Sugar Bear for the tip. I got the black end connector out through the grooves you mentioned in your last post, using a 90 degree angle hook tool by prying the groove. Thanks a lot!!!

Clarification on the 02 sensor:


In previous posts, I forgot to mention this particular 02 sensor goes downstream beyond the catalytic converter. Sorry.


Is there a difference between the upstream and downstream 02 sensors? Can I use an upstream 02 sensor for downstream 02 sensor?

While trying to get a downstream 02 sensor, all the parts stores only carry upstream 02 sensors. Then I did some research on this issue, It turns out only one 02 sensor on this 1994 Mercedes E320 wagon. Is that true? There is no downstream sensor beyond the catayltic converter in parts stores. So I assumed that the upstream 02 sensor is the one only 02 sensor and downstream 02 sensor is the one and the same as 02 sensor downstream? I thought most cars have two 02 sensors, downstream and upstream. Apparently, my 1994 E320 wagon has only one 02 sensor overall. Is this true? Feedback, comments, advice is greatly appreciated.

Cars using the OBD2 standard ( staring in 95 then mandatory in 96, the dates might move around a bit in CA ) have a up stream ( pre cat, this regulates engine fuel mixture ) and down stream ( after cat, this monitors cat efficiency. )

Wire length / plug is generally the only difference between front to rear for most cars until mid 2000 or so. Around about that time things started to get messy. Some Jeeps used a different type of sensor and Honda started to use a wide band sensor that has more wires and operates completely differently than the old standby.

The big question is, what problem are you trying to solve by changing the sensor?

I am replacing an 02 sensor on my 1994 Mercedes E320 that was broken. I thought there are two 02 sensors. Turns out to be only one 02 sensor overall and not two, am I correct?

I think just one. My 93 had only one, very similar car.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Sugar Bear, Thanks for your post. I was under the impression there are two 02 sensors, upstream and downstream. The 02 sensor is only called upstream, even though the 02 sensor is located on the exhaust bottom, basically downstream. That explains why I was never able to get a downstream 02 sensor for my particular 1994 mercedes E320 wagon in auto parts stores because it does not exist. Therefore, there is only one and only one 02 sensor overall on my 1994 Mercedes E320 wagon. Boy, am I getting an education here. I felt stupid!!! Oh well, live and learn.

97 SL320, thanks for your post. I appreciated it.

The word upstream is for before cat converter and downstream means after cat,

One cars with one sensor only, its always upstream,

New bosch universal sensors now come with a splicing connector, its fantastic to use.

P.s. some repair manuals refer to the upstream as regulating and the downstream as monitoring sensor. Also

Do not use any silicone grease on that connector, the sensor wires need to breathe.

Zulfiqar, thank you for your post. Much appreciated. All of you guys ROCK!!