4cyl O2 sensor: Bank 1 Sensor 1 vs upstream/downstream

[with0ut rem0rse]

Hi all,

My SES light came on recently and after having it diagnosed, I need to replace my Bank 1 Sensor 1 O2 sensor. It's a 4 cylinder (2003), so I know there are only two O2 sensors, but upon checking it out in my Haynes manual, the two sensors are descirbed as upstream (in the exhaust manifold) and downstream (behind the cat). Can someone please confirm which one is the Bank 1 Sensor 1?

Thanks in advance for your help.
Chris

[pinoyesv6]

i believe sensor one is the upstream one. the one before the precat.

[with0ut rem0rse]

i believe sensor one is the upstream one. the one before the precat.

Thanks for such a quick response, pinoy. That was my assumption, but it's always nice to have confirmation from those with experience. I also just found this on another website, "When the description of the code (P0135) is bank 1, sensor 1 it means the O2 sensor (pre cat) on bank 1. Bank 1, sensor 2 is after the cat."

I haven't looked yet, but I'm assuming that it can be reached from the engine compartment without getting under the car? The Haynes manual says to raise and jackstand the car, but from what I've read on these forums, it doesn't seem to be that complicated.

Thanks again.

[UAL Tripple 7]

Keep us informed on how easy or hard it is to replace the o2 sensor. This is the one I have to replace on my ride too.

[bronxbombr]

i sell the O2's if you wanna buy em.

[with0ut rem0rse]

Keep us informed on how easy or hard it is to replace the o2 sensor. This is the one I have to replace on my ride too.

UAL Tripple 7 - I just got in from replacing the upstream (Bank 1 Sensor 1) O2 sensor. I have a 2003 ES 4 cyl, and the O2 sesnor was right in front of me as soon as I opened the hood. My Haynes manual said to jack up the car and put it on jackstands - totally uneccesary (unless I replaced wrong one?!). It's very easy to get to. I also bought an O2 sensor socket, but I think it's possible to get a wrench on the sendor without spending the money for the socket. hope this helps!

bronxbombr - when I was searching the forums for help on this, I saw a few of your posts where you said you had the sensors. I wanted to get a direct replacement part, and I thought you were selling the universals.

[with0ut rem0rse]

Hi,

To close the loop on this issue, and to hopefully put everything in one place for the next guy searching for this issue, I wanted to clear my SES light after the O2 sensor install. After searching a little, I found this excellent thread: clear DTC codes (SES light) without using a Scantool

[Calipso]

For o2 censors, does it matter if you go Mitsubishi OEM parts or generic ones from autozone/advanced auto parts?

My car has been really sluggish lately, and I need to some routine maitenence.

[pinoyesv6]

if you get an oem replacement part, its just plug and play. if you get a universal sensor, you're gonna have to splice it in.

[Calipso]

if you get an oem replacement part, its just plug and play. if you get a universal sensor, you're gonna have to splice it in.

Good to know, going to have to keep that in mind.

[bronxbombr]

no i get direct and universal replacments.

[solofantasy]

I have the same problem now.

So after you replace it with a New O2 sensor, does SES go out by itself, or i have to reset ECU??? anyone? or do I have to use Scan tools?

[pinoyesv6]

I have the same problem now.

So after you replace it with a New O2 sensor, does SES go out by itself, or i have to reset ECU??? anyone? or do I have to use Scan tools?

when working on your car, especially on something that has wires, you should disconnect the battery anyways just to be safe. so that should rest the ecu and clear the code.