03 montero limited - I recently replaced an upstream o2 oxygen sensor due to throwing CEL during driving. The CEL identified the faulty oxygen sensor. The heater element did test bad so I knew it was time to replace. Instead of the $300 OEM sensor, I bought a Bosch universal. Twice since replacing (4 days) Ive gotten 2 CELs - both being P0300 - multiple misfire code. A few sites I checked says thats it generic and that it could be a number of things including oxygen sensor. I checked all the wires around the nstall to verify that I did not bump something loose. All looks good. Im thinking if I continue getting this code, Ill suck it up and get the OEM 02 sensor. Ive nver had this CEL before so Im thinking that its strongly the sensor.

Anyone with experience with this or trouble with universal sensors? I thought all o2 sensors were equivalent, bouncing btw 0-1 volt depending on the exhaust gas....

UPDATE: I bought a Denso OE sensor (234-4742) today, so Ill replace to see if the p0300 code goes away. I wish I kept the old oxygen sensor so that I can reinstall it to see if the p0300 code goes away and the o2 sensor CEL comes back. The Denso unit was $120 w/ ship , still less than the online stealerships @ $260...

Before I would assume the sensor is bad I would check either on the bench or better yet installed. From my research the aftermarket ones are better than OEM because they have a faster responce times and are more stable.

I know this is probably a silly question but are you sure you connected the leads correctly? I ask this because I found conflicting info on which lead and colour was what. You should be able to confirm by testing. I've attached a site below on the operation and testing and another on sensor wires which may offer some clues.

http://auto.howstuffworks.com/framed.htm?p...G/o2sensor.html

http://www.lambdasensor.com/main/mcolours.htm

Good luck and please report back on your findings. Most of us will be replacing ours in the not to distant future.

Jim

Jim: Good ideas - Ill recheck the wiring. I understand that you can damage the sensor if its polarity is reversed. If I got the wiring wrong, I guess the sensor is trashed.. I know that I triple checked this during install, but I am human....,

I don't think you will stuff the sensor. The heater can be connecet either way it doesn't matter. Ground wire and sensor are ussually colored and if you get wrong it still may be OK. Check fuses and may need to clear ECU if wrong. Study up on the connection diagrams and re-check wiring first.

Jim

I think that universal HO2 sensors are work of Lucifer. They are never accurate and i see many people improperly wire them accidentally. Ive never used one before for this specific reason of fixing these issues caused by universals. Besides teh life span and accuracy to the OEM is not exact. I do not reccomend using a universal on a HO2 (heated oxygen sensor ) system.

My replacment sensor of choice is the Nippondenso , the are cost efficient and the lifespan is better than that of the Bosch , not to mention cheaper. The factory ones here are all ND and not Bosch anyway.

I checked the output of both upstream sensors this morning. I noticed that the BOSCH universal takes longer to "activate" when cold versus the factory upstream sensor. Also, while running, it seems that the BOSCH unit does not bounce as rapidly between 1 and 0. In fact, there are long periods where the sensor seems to stay at either 1 or 0. On the screenshot below, the BOSCH unit is on the right and the scale is 1 ot 0 volts.

I also notice that both sensors are inverse of each other. When factory sensor is at 1, the bosch is generally at 0. Is that behavior normal? I dont see how each side of the motor would be opposite from each other.

I also verified the correct wiring according to the links above. The mitsu wiring is the same as the toyota version on that website.

The thing ive notices is that , as OEM sensors pre heat right on at cold start and set situations the universals do not. As stated it does seem to take longer on the universal, the fact to that is because of the element type and design because it is a universal.

Also they do not gauge small windows of regulation the way an OEM does is why people do have issues with them even when they are wired correctly. On some older models 1996 down yu can sumwut get away with it for a period of time but 1998 up systems are alot more strict on the variables that the sensor sends to it. Most of the according systems have a very small variance window to alow as with the older systems.

Good points and thanks for the help. Today I found the original O2 sensor in the trash and its still in great shape. If I get a chance, Im going to reinstall the original sensor to see if I can stop the P0300 misfire CEL. I can live with the original CEL that indicated a heater malfunction. I cant however live with the latest "random cylinder misfire" CEL after I installed the universal.

I also going to check if the Left and Right banks really are inverse of each other when both OE sensors are installed.

I managed to fish out my receipt for the BOSCH universal so Im going to try getting my money back on this. Im going to bring the output graph with me to help my case. I know the parts store is going to give me trouble in trying to return the universal.

Ill post results as well as comparison with the new ND sensor that is being shipped to my house right now.

Thanks for the ideas everyone.

This is all good info to know. I have only experimentated with O2's my older 91 MR2 and not with the newer Mitsi yet. Keep us posted on the results as it will be of interest to all.

Jim

Frum wut i am getting is that , one of the HO2 sensors on one of the banks is either making the fuel injectors spray too much gas or not enough. While one may be pretty much within the desired range it has the fuel injectors on that side of the engine delevering fuel correctlly. Altho there is an issue with one , the computer is adjusting teh fuel spray on the side with the sensor that is giving it readings that are out of range. So like to say the left 3 cylinders are getting proper fuel to air , but the right bank isnt .

Ive been thru this there are 2 totally diff upstram sensors and 2 diff down stream sensors on these models. example. Generally the left and right bank up stream sensors are the same. And both down stream sensors are the same. NOT

Thats why i tell people use OEM NipponDenso replacments on the sensors LoL. The sensors are reversed on 1997 up models. Because of the differance in the length of the crossover pipe to teh catalytic converter , which there are 2 the heat rate would be diff on the upstream and down stream sensors. Generally the left bank and right bank upstream sensors are diff , so are the downstream.

Right side upstream sensor is actually placed downstream after the catalytic converter(planar) and the downstream at the upstream position , its reversed because of the differance in length to the dual catalytic convertors. The miss is because one bank of cylinders is not getting enough gas at times and too much at other times

Huh?? I'm going to think about this one for awhile. Little confused on how the sensor can be reversed, do you mean wires are connected differently?

As far as I know all O2 sesors are basically the same. Some may work better and have quicker responce time or have a heater but the acual Lambda sensor is the same unless of course it is a wideband which only performance cars with mod ECU can utilize.

Jim

I think I understand what Kit is saying.

I want to reiterate that the left bank has the universal O2 sensor. The left bank has the short pipe to the catalytic converter. The upstream left bank O2 is closest to the pistons. The right bank upstream is further away from the right bank pistons. The right bank upstream is actually below the truck on the cross over pipe to the catalytic (which is located on the left side of the truck). Is that why both upstream sensors are inverted? - the distance to the pistons are different. If so, that is pretty cool...

I compiled pictures of all 4 nippon o2 sensors with PNs:
http://docs.google.com/Doc?id=dgs45h5n_11qdhxzqc2

Look at the bodies and plugs. Both L&R upstream bodies look the same and downstream L&R bodies are the same. However the plugs are inverted. The upstream R plug looks like the downstream L plug. I think this is what kit is talking about.

Im starting to think that not all o2 sensors are the same. Not only the heater elements but the response times and calibrations etc. Kit make sense about how the left side of my motor is either getting too much or not enough fuel if the universal is not sending the right data to the ECU.

NO , there are 2 diff. Look at it at this angle. Standing in front there is the right bank of the engine and the left bank . The right side exhaust downpipe crosses to the left side. Both catalytic convertors are on one side . The left. The reason is that because the driveshaft for the 4WD passes on that side so there is no room for the catalytic converter.

So both catalytic converters have been placed on the left side. But with the right bank catalytic converter being farther away , the upstream sensor will not heat up as fast as the left bank upstream sensor because the catalytic converter is a shorter distance.

Now do yu see? on the left side the engine the catalytic convertor is not far frum the sensor , so the sensor will heat up rather quickly . But the right bank converter is far frum the sensor so it wont heat up at the same rate as the left side .

Turn it around the downstream sensors on the otherhand , being after the catalytic convertor , the right bank catalytic converter will heat up sooner and more than the left bank converter since it is farther away frum teh manifold. basically it traps heat. So the right bank down stream sensor will heat up faster and higher than the left bank downstream sensor.

Just to aide this TJ90 inspect the plug ins on both yur downstream HO2 sensors , i bet the plug ins arent the same, altho a parts house will sell yu the same downstream sensors and yu will have issues when yu install them cause one will not plug in

Yuve hit dead on wut i am saying LoL, yes teh inversion is due to the distance

Kit - I reread what you wrote 10 times. Everything makes sense except the part where you say the right side downstream 02s will heat faster. How can the right downstream heat faster if the distance from the downstream o2s to the cats are the same for both sides?

I looked at the schematics for the truck and it appears that the upstream o2 sensors are placed the same distance to the headers on both sides. The difference, as you point out, is that the left cat is much closer to the upstream 02 and the headers. Funny that even though the left upstream o2 should heat up faster, I still have slower response from the heated BOSCH universal. The heater elements are slower than OEM ND for sure.

The message for the viewers at home is replace with OEM!!! Who would have thought that a simple component could mess up the truck so much!

Still dont know why both sides appear to have inverse relationship. I will install the original L-Up o2 sensor and see if its still appears to be inverted...