o2 Sensor Loacations...

[XpL0d3r]

Having a dispute with my mechanic lol... I have a CEL for catalytic efficiency below threshold (code P0420)... after I got my header and new cat installed.. I noticed BOTH of my o2 sensors are on the header, in front of the cat. One should be in front, the other should be behind correct? Because one should be checking to make sure the cat is functioning properly.. and if in front of the cat it doesn't even know what to look for, right?


Car is in the shop right now getting a new o2 sensor bung welded on BEHIND the cat... should fix my problem I hope right? The guy who's doing it disagrees with me though... so I need some verification to see if I'm right or wrong lol.

 

[hardcore97]

my car had one in the header and one in the cat. at the end of the cat IIRC but yes one is supposed to be after the cat or in the cat like the stock cat has it.

 

[31dev31]

You are correct. The guy who disagrees with you is a moron.

 

[Szady]

Shaun....here's some advice. NEVER bring your car to the shop its at right now. EVER.

1 o2 sensor before the cat, in the header. The 2nd o2 sensor AFTER the cat (or in it towards the end of it) so the ECU know's how rich/lean the car is running.

/thread

 

[vandynamics]

just because some random grease monkey doesnt know o2 sensor location on a honda civic doesnt mean hes a moron. in his defense, that guys job is to fix cars... specifically ANY cars.

 

[clover ej6]

just because some random grease monkey doesnt know o2 sensor location on a honda civic doesnt mean hes a moron. in his defense, that guys job is to fix cars... specifically ANY cars.

amen

 

[XpL0d3r]

Well, he IS a good mechanic, for the most part. Does a lot of free s**t for me ha. He's currently in the process of turboing his honda too. He just doesn't know o2 sensors i guess lol.

Anyways, I got the secondary sensor moved to a spot on the cat. I had to extend the o2 sensor wires myself a good 30" to make it reach lol. Hopefully my CEL doesn't come back.. I have inspection/emissions that was due in May that i need to do...

 

[Szady]

just because some random grease monkey doesnt know o2 sensor location on a honda civic doesnt mean hes a moron. in his defense, that guys job is to fix cars... specifically ANY cars.

Well, if he fixes ANY car, he should know that the first o2 sensor is before the cat, the 2nd is after. Its pretty COMMON KNOWLEDGE for any gasoline engine. I dont know of ANY car that runs two o2 sensors BEFORE the cat, and none after it...

 

[hardcore97]

Well, if he fixes ANY car, he should know that the first o2 sensor is before the cat, the 2nd is after. Its pretty COMMON KNOWLEDGE for any gasoline engine. I dont know of ANY car that runs two o2 sensors BEFORE the cat, and none after it...

every time ive bought an o2 sensor for any car they always ask if the one before or after the cat at the parts store when i order it

 

[NOFX]

Having a dispute with my mechanic lol... I have a CEL for catalytic efficiency below threshold (code P0420)... after I got my header and new cat installed.. I noticed BOTH of my o2 sensors are on the header, in front of the cat. One should be in front, the other should be behind correct? Because one should be checking to make sure the cat is functioning properly.. and if in front of the cat it doesn't even know what to look for, right?


Car is in the shop right now getting a new o2 sensor bung welded on BEHIND the cat... should fix my problem I hope right? The guy who's doing it disagrees with me though... so I need some verification to see if I'm right or wrong lol.

Is your car a DX, EX or LX?

DX and LX have both oxygen sensors on the "header". The cat is built onto the bottom of the header and technically the secondary oxygen sensor is AFTER it (sort of under it).

EX has one oyxgen sensor up front on the header, and then one on the back of the cat under the car.

Your mechanic is correct unless you changed a lot more on your exhaust.

DX/LX / D16Y7

EX / D16Y8

 

[Szady]

Is your car a DX, EX or LX?

DX and LX have both oxygen sensors on the "header". The cat is built onto the bottom of the header and technically the secondary oxygen sensor is AFTER it (sort of under it).

EX has one oyxgen sensor up front on the header, and then one on the back of the cat under the car.

Your mechanic is correct unless you changed a lot more on your exhaust.

Reading > you. He said BOTH o2 sensors, are on the header, INFRONT OF THE CAT (the NEW header, and NEW cat, kind of makes one thing neither are OEM). Either way, the mechanic is wrong.

 

[NOFX]

Having a dispute with my mechanic lol... I have a CEL for catalytic efficiency below threshold (code P0420)... after I got my header and new cat installed.. I noticed BOTH of my o2 sensors are on the header, in front of the cat. One should be in front, the other should be behind correct? Because one should be checking to make sure the cat is functioning properly.. and if in front of the cat it doesn't even know what to look for, right?


Car is in the shop right now getting a new o2 sensor bung welded on BEHIND the cat... should fix my problem I hope right? The guy who's doing it disagrees with me though... so I need some verification to see if I'm right or wrong lol.

So is this supposed to be an aftermarket header?

Again, what car? I'm guessing it has a D16Y7, but it was never made clear in the thread.

I've never seen an aftermarket header like that, but I'm not into Y7 parts.

What exactly is it that the mechanic believes then?

Reading > you. He said BOTH o2 sensors, are on the header, INFRONT OF THE CAT (the NEW header, and NEW cat, kind of makes one thing neither are OEM). Either way, the mechanic is wrong.

Why would there be two O2 sensors in front of the cat to begin with anyway?

I know how it's supposed to be. I just don't understand his description.

 

[DarkCreep]

What exactly is it that the mechanic believes then?

Why would there be two O2 sensors in front of the cat to begin with anyway?

I know how it's supposed to be. I just don't understand his description.

Because most bolt-on headers for D16's have both bungs for the o2 sensor on the header itself.

 

[Szady]

So is this supposed to be an aftermarket header?

Again, what car? I'm guessing it has a D16Y7, but it was never made clear in the thread.

I've never seen an aftermarket header like that, but I'm not into Y7 parts.

What exactly is it that the mechanic believes then?

Why would there be two O2 sensors in front of the cat to begin with anyway?

I know how it's supposed to be. I just don't understand his description.

Car is a LX, with a Megan 4-2-1 header, and a basic stock exhaust. He's saying, BOTH of his o2 sensors are infront of the cat. One sensor is in the #4 runner right off the head, and the 2nd is INFRONT of the cat in his exhaust. That 2nd o2 sensor needs to be AFTER the cat in the exhaust. Any mechanic with even the littlest bit of common sense, can look at the header and see, theres no cat in there.

 

[XpL0d3r]

Even though the car is an LX, the head, header, etc is all from/for an EX.

I got a new o2 sensor bung welded into the cat, had to extend the o2 sensor wire myself a good 30 inches. The OTHER mechanic I brought it to who did the welding, kept my car on the lift overnight.... with the keys in it and turned one click... AKA dead battery the next morning.

Anyways, sensor is in his new location, 30" away from where it was before... no CEL at allll. Now I just gotta get a new tie rod and I should be set for my late inspection lol. My driver side front wheel can literally move like a half a centimeter sideways...

btw: here's what it looked like:

the primary sensor was where it should be. no problem. the RED dot was where the o2 sensor USED to be (before I posted this thread)... aka incorrect because it's supposed to read the cat. When I talked to my mechanic, he said it shouldn't matter. This is where he was wrong. He is a very good mechanic and really knows his stuff, I've gone to him many times so no worries there. Only human I guess, lol. The correct spot (other green dot, on the cat).. was where the sensor was moved to.

Problem solved.

 

[wannabe]

you should actually move the primary sensor down to where the secondary one used to be. you want the sensor to be getting a reading from all four cylinders. if its just in the runner for the no. 4 cylinder its not providing accurate info for the whole engine.

 

[DarkCreep]

you should actually move the primary sensor down to where the secondary one used to be. you want the sensor to be getting a reading from all four cylinders. if its just in the runner for the no. 4 cylinder its not providing accurate info for the whole engine.

This man is 100% correct.


I wanted to do the same, but I just got the extension since it was easier.

 

[XpL0d3r]

wellll i may do that then lol. Thanks for that. It's just a plug in the old bung, so I can pop that out, switch the sensor location, and plug the top onee I suppose.