o2 sensor placement

[cocolizo]

hello, posting the question for my brother. anyways he has a 03 civic lx and hes been having a lot of issues with the check engine light poping up over nd over again. catalytic converter related, he first had the original which gone bad and needed to be replaced so he instead went for a new complete cat-exaust system. this had the catalytic attached to the manifold just like OE. it would still pop the engine light again saying it was a misfired or something, turned out to be that one of the bolts from he header broke inside the head so there was a leak coming tru the header. he got that fixed but still would give him the light. after spending so much money already he got tired and went nd buy them separetaly, he bought the header then a cat that goes in placed where the down pipes is but now the shop says the he has to extend the o2 cables because the cat is more in the middle of the car not close to the engine like the original was and that it would still give the o2 sensor light because they say that those cats are made to be close to the engines not all the way in the middle so they wont read correctly and would give him a code for bad o2 sensor. all this parts are supposed to be made for his civic lx so my questions is why would they sell a catalytic placed differently than the original if its not gonna work??? or ima missing something here ??? any help would be much appreciated

 

[Gunner]

Can you find out what the code is like the numbers? Also if the parts you got are OEM then i dont see why you would have to put them in a different spot unless they ordered the wrong parts. People extend the 02 wires but usually only when they modify or swap motors.

 

[99coup3]

Make sure that the sensor is at the back of the cat. That was the problem I had.

 

[cocolizo]

well, just to clarify things i just look at the cat and it is actually an universal catalytic but its advertised and sold to fit civics LX , he bought it on ebay . so its not placed in the same spot as the original. its actually further down the exaust, kinda in the middle like the old cars . the shop people say that since the o2 is far down the exaust it wont read them. the header has to holes and the cat has one hole before and another after the cat so theres no issue with them it just that distance from the engine to the cat that they say its not gonna work, i think it doesnt make sense

 

[Gunner]

people move the sensor all the time when they do swaps..you have to extend the wire...there is a chance it wont work but most of the time you will be fine...but the sensor has to go after the cat...but the wire needs to be longer..doesnt hurt to try...otherwise buy yet another cat and get the stock oem one...

 

[XpL0d3r]

^ Correct. One sensor (primary) will be in front of the cat, and the other will be on or behind it (Secondary). This is how the ECU knows your cat is functioning properly... it will read the first sensor, and compare the readings to the second sensor. Obviously because of the cat the readings will be different, and all is well. if you have both sensors on the same side of the cat they will read the same, thus the ECU thinks the cat (or o2 sensor) is not functioning properly, and will throw a CEL at you.

I had to extend my secondary o2 sensor almost 3 feet. I don't worry about that now though since I'm running open loop..