00-04 BE/BH Oxygen Sensors

[ryankenn]

I'm going to replace my two O2 sensors ( front and rear ) but I'm hoping I can find a Bosch or other replacement or universal part to avoid spending $100+ each.

From this schematic:

https://sl-i.net/FORUM/ (http://img241.imageshack.us/my.php?image=98802979jm1.gif)

I'm assuming the rear is 4 wire and the front is 6??? I'm no expert on O2 sensors but I'm heard of 1,2 and 3 wire, and now I've seen some 4 wires on Ebay, but 6 wires?

Has anyone replaced theirs with no OE universal types that can help me out? Do the sensors come with a description of what the wires do so they can be matched up with the Subura factory wiring?

Any info would be helpful.

Thanks
Ryan

[Huffer]

I'm no electrician either, so I would just slide under the car and grab the boot of the plug, slide it up and count the wires/colors.

[jmgtp]

They are both 4 wire sensors.

I've replaced both of mine. The car didn't mind a Bosch universal for the rear sensor but the Bosch universal front sensor tripped the CEL (yes it was wired correctly!). I replaced the front sensor with an OEM Denso (comes with correct harness / $100 @ sparkplugs.com) and the CEL went away instantly.

The reason I replaced was due to a P1133 CEL - an ohm meter verified that the heater element on the front sensor was an open circuit (burned out).

If I recall correctly the Bosch universals will tell you what colors the wires on the Bosch sensor relate to... but it is up to you to know where to wire them into the Subaru harness, you should be able to figure it out with a volt/ohm meter pretty easily. I just did mine last month but do not recall which colors correspond to which function - I do recall both front and rear sensor used the same wiring color schemes for the same functions.

[SammyDaFish]

like jmgtp said, the factory O2 should be a Denso one and they should only be about $100 with the factory connector. It's worth getting the right one for the front sensor. The o2 plays a big role in fuel economy and power, having one that works perfictly is worth it. The rear you can get a universal one for, but even that you only need to replace if it throws lights the MIL and dirrect replacement ones are only like $70-$80. Pretty sure Subaru has used the same rear O2 since 95 on all models.

[ryankenn]

I'm in the process of buying these and sparkplugs.com only shows the rear Denso part, no front one is listed?

Is there any other online source for these at a reasonable price?

[SammyDaFish]

what are you trying to look up? They have them both, make sure you get the right one too, the plug changed in 03 and the O2 has a different part number (though I think the base sensor is the same)

[ryankenn]

I'm using my car for specs

2002 Legacy GT Auto, 2.5L.

Under O2 Sensors for Denso, it only shows my the rear sensor, no front available. I also looked under 2001 and 2000 with no luck either.

[ryankenn]

What I found most distressing this evening was searching Denso's on online parts catalogue, where I was again greeted with only the rear Sensor being listed for my 2002? Also, for 2001 and 2000 they list a front one, great, except its only listed for the manual tranny car, not my auto.

What's going on?

http://www.densoaftermarket.com/catalog ... del=LEGACY (http://www.densoaftermarket.com/catalog/catalog.php?part=o2sn&year=2002&make=SUBARU&model=LEGACY)

If anyone can point me to a link to buy a sub -$120US front O2 Sensor with the OE plug you'll have my thanks.

[jmgtp]

rockauto.com list one for $120

-denso #2349018

they do not list a different front sensor for manual/automatic. Perhaps they are the same in 2002? I imagine the only difference may be wire length - the one listed above is 14.96"

[ryankenn]

Finally just phoned Subaru to get it from the source, found this.

Front - $141CAD - 22791-AA00A ( not considered an O2 to Subaru dealerships, considered the A/F Sensor )

Rear - $232CAD - 22690-AA73A ( this is the P/N AllData fed me as being the Front O2 Sensor, and had an MSRP of $119US )

So it seems that according to ALLData, there isn't a "rear O2" sensor, there's just the one O2 sensor, as under sensor, I found the above A/F sensor P/N for in front of the cat.

Weird.

[SammyDaFish]

( not considered an O2 to Subaru dealerships, considered the A/F Sensor )

that's common on most cars built around 2000 and up when manufacturers started using wide band sensors to meet stricter emissions standards. Different catalogs and repair manuals list it differently so sometimes it's confusing trying to find the right part.

[ryankenn]

I managed to get both. The A/F was only $140 from Subaru, and the rear I got for $130 from oxygensensors.com. Both fit with no problems.

What's interesting is my new 2.5" SS exhaust uses a high flow magnaflow cat that's too big to be near enough to the header exit to get the sensors on either side of it, so they just put both right next to each other. A/F first, then rear, both in front of the lone cat.

To my surprise its been about 1.5 weeks and no CEL? Does the car not take some type of difference reading between the two sensors to make sure a cat is active?

Curious?

The car is louder now, but revs way quicker and has alot more giddie up with the new exhaust. And you can't beat the look of 2.5" SS mandrel bent pipe!

[SammyDaFish]

the thead where the 2nd O2 goes is probably taller than the primary right? This is a common trick for those that run catless. The O2 is partialy shrouded from the flow of the exhaust and reads slower and leaner because of it. Doing this usualy works, but even having both O2s on the same side of the cat makes it no longer street legal, so why even run a cat?

[ryankenn]

Maybe where you are!! Mine passed the sniffer Aircare with the setup last week. They take about a two second look with a mirror to make sure a cat is under there, I highly doubt in our system of testing they even know what else they are looking at.

2.5 weeks now, and still no CEL. Both bungs are the same height. I may extend the harness anyways just to try and achieve a more factory like environment.

[Wiscon_Mark]

um, what's the point of having them both on the same side though? It's not like you have less restriction.

[ryankenn]

=magnaflow cat that's too big to be near enough to the header exit to get the sensors on either side of it


um, what's the point of having them both on the same side though? It's not like you have less restriction.


The rear one's wires weren't long enough to reach past the cat, so the shop just bunged it in on the same side. Do they actually take a differential reading between the two to tell the car if the cat's functioning? The front one is responsible for A/F so I don't think this effects how the car runs in terms of rich/lean but I thought for sure it would signal the car to display a CEL.

[Wiscon_Mark]

The rear o2 sensor measures how efficient the cat is, and has a lot to do with the A/F ratio as well. It does a lot more than the first sensor, from what I've read.

[ryankenn]

Hmmm, maybe that's why it costs so much more up here.

I think I'll move it to the other side of the cat with some extended wires if it is at all responsible for the fuel mixture.

[SammyDaFish]

The rear o2 sensor measures how efficient the cat is, and has a lot to do with the A/F ratio as well. It does a lot more than the first sensor, from what I've read.

nope, the rear sensor simply checks cat efficiency for OBD2 compliant emissions self diagnostics. The front o2 gives feedback for engine performance, that's why on most newer cars it's actualy a wideband sensor and is called an A/F sensor now, not an o2 anymore, even though it's essentialy a wideband o2.

The second sensor does nothing for engine performance unless it sets the MIL and triggers limp mode.

[Wiscon_Mark]

hmmmm, okay. That contradicts what I've been reading on Nasioc, but there's a lot of misinformation there as well.