O2 Sensors

[dbaxRonin]

So I am long overdue to replace two bad O2 sensors. I have to take an emissions test this year and will certainly fail if I don't address them, and would like to do it while the weather is still decent enough to work in the garage. I have to go back to the auto store and get another scan to find which two are bad since I forgot to write the codes down last time.

Wondering a few things. First, is it best practice to just replace all 4 at the same time...if two have gone to pot I imagine the other two aren't far behind.

How hard is it for someone handy with the tools but not much experience working on cars to replace them all? Do I really need a special O2 wrench to get them out?

The auto-store wanted $150+ for each sensor. I see they can be had online for much cheaper, but there are so many to choose from. Any particular brand I should key in on or avoid? Is there a particularly good site to get them through?

As I perused various online retailers, one thing confuses me. A number of them list options for "primary" and "secondary" catalytic converters. Per the attached photo that I snagged from the FSM, I only see one sensor in the manifold downpipe, and two on what I would presume to be the "primary" converter (labeled "Front exhaust tube assembly" in photo). Is the "TWC (under floor)" the "secondary"...and if so I see no sensor attached to it. And what of the sensor that is on the manifold...how would they classify that? I just want to be sure to order the right sensors, and with all the different verbiage used, it is confusing as to what goes where.

Lastly, after they are all replaced, will I need to have my ECU reset to get rid of my SES light and clear out the error codes...or will it pick up on them and just reset itself after a while of driving?

Thanks a ton for any help!

[audtatious]

You can probably replace front pair or rear pair together but I would not replace just one at a time or a front+rear unless they are the same brand as they could communicate differently to the ECU and still throw codes. I have seen people have issues with generic and no-named sensors. NTK seems to be a good brand to get and possibly Denso. As I have not replaced any I'll leave it to others to chime in on which brand is the best to use.

[tigersharkdude]

I personally always go with Denso

[dbaxRonin]

Bank1 Sensor 1 (P0134 - Front - High Input), and Bank 2 Sensor 2 (P0160 - Rear - High Input) are the ones coming back bad on the scan. Naturally the two hardest to get at.

You know, the more I look at these parts, the more frustrated I am becoming at trying to determine the different verbiage used. I referred to a great post by Loystock over in the thread (Link) that you get to when clicking on the links posted for the O2 sensor SES codes, but there are still a few things that befuddle me.

First, you have Bank 1 (Firewall) and Bank 2 (Radiator). It seems different places use the terms Front and Rear, and Upstream and Downstream, in different contexts. As per the image I posted in my first post, Infiniti has used Front and Rear to determine Upstream (Front/Precat) and Downstream (Rear/Postcat). But then I look at online part places (i.e. OxygenSensors.com) and they use terms like "Precat - Front" AND "Precat - Rear"...almost as though Front and Rear are relating to Bank 2 and Bank 1.

Another place I was looking (RockAuto.com) has "Downstream Front" and "Downstream Rear", and "Upstream Front" and "Upstream Rear"...again making me think that they consider Front/Rear to be Bank 2/Bank 1. If "Front", according to Infiniti, is the Upstream...how can you have an "Upstream Rear"? Conversely, if "Rear" is Downstream, how can you have a "Downstream Front"?

And don't even get me started on the whole Left/Right and Driver/Passenger BS!!

If I had to wager a guess, I would say these online retailers are listing "Front" as Bank 2 (i.e. Radiator = toward Front of vehicle), and "Rear" as Bank 1 (i.e. Firewall = towards Rear of vehicle)? Things start to fall into place with that logic a little better, but there is nothing I can find to solidify this theory.

Sorry that I am asking so many questions here, but this lack of standard naming is really throwing me for a loop and I would like to understand all this better. Ultimately I will probably replacing all 4 sensors, so as long as I get 1 of each I should be OK, but I would still like to get this all straightened out. TYIA!!

[audtatious]

Upstream/Front are before any catalyst. Downstream/Rear are post-catalyst. The exhaust system of the Maxima/I-series have two pre-cat's as part of the exhaust manifold/y-pipe along with the main catalytic converter. Uptream/front are before the pre-cats and downstream/rear are after them. All O2's are before the main catalytic converter.

The Left side of the motor is Front and the right side of the motor (firewall area) is Rear.

[dbaxRonin]

See...I get that, but that still doesn't explain a term like "Rear Upstream" or "Front Downstream" when there are two definitions for the words Front and Rear at play. Basically you end up with Front (radiator)-Front (Upstream), Front (radiator)-Rear (Downstream), and, Rear (firewall)-Front(Upstream) and Rear(firewall)-Rear (downstream).

Perhaps Infiniti as at fault here for defining "Front" as Upstream and "Rear" for downstream??

I am probably over-analyzing this too much...I suppose it's a tendency I have thanks to the type of work I do (programming analyst). I am going to go with Front meaning Bank 2 and Rear being Bank 1, then upstream being pre-cat and downstream being post-cat and call it a day! Thanks for the help audtatious! /me throws in proverbial towel

[audtatious]

Front and Rear are simply definitions for left and right sides of the transversely mounted motor.

Imagine you are sitting in a RWD car and the motor is mounted longitudinally under the hood. Looking over the hood the motor has a left and right side (which is opposite if you are standing in front of the car looking at the engine). Now, if you turn that motor to the right, where the front is now facing the passenger-side, the left side of the motor is not the front and the right side of the motor is the rear. If you pop the hood and stand at the drivers-side wheel overlooking the engine then the left side (radiator) is your left and the right side (firewall) is the right.

From a "bank" perspective:



Banks change things completely it seems:
Bank 1 front sensor 1 is the rear/right upstream
Bank 1 rear sensor 2 is the rear/right downstream
Bank 2 front sensor 1 is the front/left upstream
Bank 2 rear sensor 2 is the front/left downstream

[dbaxRonin]

Thanks again aud...that confirms my thoughts on all this, and that is a great image...hopefully others will benefit from this as well.

I think I have bigger fish to fry now however. I setup the car to get under it to try and get a better look at the location of the sensors and I was disgusted at what I saw. It appears my car is rotting away a lot worse than I suspected. I knew the front frame cross member was rotted out a fair amount, but it has gotten to the point of dangerous. My passenger door sills have also gotten so bad that when I simply went to push on it to feel for sponginess, my finger went right through it like it was warm butter. I couldn't even find a spot I felt comfortable enough with to use the floor jack on. I reckon that I might actually have to try and find a new car.

[NutriaforBreakfast]

Am running Bosch O2 sensors in my 98 and 95
No problems with them

[audtatious]

Thanks again aud...that confirms my thoughts on all this, and that is a great image...hopefully others will benefit from this as well.

I think I have bigger fish to fry now however. I setup the car to get under it to try and get a better look at the location of the sensors and I was disgusted at what I saw. It appears my car is rotting away a lot worse than I suspected. I knew the front frame cross member was rotted out a fair amount, but it has gotten to the point of dangerous. My passenger door sills have also gotten so bad that when I simply went to push on it to feel for sponginess, my finger went right through it like it was warm butter. I couldn't even find a spot I felt comfortable enough with to use the floor jack on. I reckon that I might actually have to try and find a new car.

Holy crap, poor car

Looks like you have a whole lotta work to do if you want to keep that one around for a while.

[loystock]

That's the lower radiator support. Per link below, the last post by 'nafddur" stated that it was replaced for @ $400.

rust-on-radiator-support-t510465.html

As for the O2 sensors, I use NGK/NTK. I have replaced 1 in 97Q45; 2 in 99I30 and 1 in a 97I30. If you know the part number, you can buy it cheaper from Amazon.