O2 sensor secondary

My engine light has come on a lot of times saying its my cat, but would always go away. Recently its been on continually and has also added a code for the secondary O2 sensor. When I got my timing belt replaced at the dealer he said the O2 is about 300 to replace and the cat was covered. My thinking is that the O2 isnt bad, the computer just says that because the cat code comes on so much. Unfortunately the dealer cant get the cat for 3 days, because its such an incredibly rare part, so I have to schedule another appointment for them just to replace the cat. Any ideas on what to do with the O2. Keep in mind Im a broke college student.

Why would your cat be rare? And what do you mean by "My engine light has come on a lot of times saying its my cat", do you mean it come up with the primary O2 sensor code? If it is your cat that is bad, it can cause your O2 sensor to go bad as well.

I was being sarcastic about being rare. The light would always come on and I ran the code, just the cat code, the light goes off, comes on a month later, ect. Eventually the code for the O2 came on as well. I guess the cat killed it, but how can it do that?

because if your catalyst efficiency is below threshold. it means all that pollutant junk has clogged your cat. your o2 sensor is plugged in there too. thats why it will crap too.

go pick up a universal denso o2 sensor off ebay and take your cat in to be replaced if it is covered under warranty. when the cat is in, replace the o2 sensor yourself.

just curious, what car is this?

This is a 98 civic. Good plan, I've already lined up the cat replacement. How simple is switching the O2? Would you be able to tell me how to do it?

This is a 98 civic. Good plan, I've already lined up the cat replacement. How simple is switching the O2? Would you be able to tell me how to do it?

a 22mm wrench and a junction plug. i bet my 8 year old newphew could do it.

This is a 98 civic. Good plan, I've already lined up the cat replacement. How simple is switching the O2? Would you be able to tell me how to do it?

Hey Driftking, Just a side note. First your car has two ho2s (heated o2 sensors) one before the cat, one after.

I would check your cat first before you repl it, being it's a 98 it should still be good if you haven't been abusing it too much. or ran too long with the CEL light on

The reason you are getting the cat code is the second o2 is reading a fluxsating o2 reading. This could be because the first o2 has slowed or is baised rich or lean and your cat isn't working right (not storing enough o2)

Have you checked the output of the ho2s? You will need a ocilloscope
to check them. They operate to fast for a normal DVOM

I would check them first before you put on the new cat, as if you don't the new cat will end up like the one you allready have, if it is actully bad

Sorry for the spelling errors I don't feel like looking them up

Smoghog

ill make it simple for you.

reset the ecu. if the cel comes back as catalyst effeciency and secondary o2, then they are both gone.

youwant to physically check the cat and o2 sensor? drop out the cat and look through it. if you can barely see anything or nothing at all, then it is gone.

Have you checked the output of the ho2s? You will need a ocilloscope

this isnt your high school science lab. simplicity = go get a cheap and simple voltage and continuity meter from walmart, kmart, walgreens, or riteaid. measure and compare to specs.

The reason you are getting the cat code is the second o2 is reading a fluxsating o2 reading. This could be because the first o2 has slowed or is baised rich or lean and your cat isn't working right (not storing enough o2)

actually, there are many reasons as to why the cat will go bad and get clogged. i believe whatyou are trying to say here is that the primary o2 sensor can go bad and throw a cel (problem here is, there is no cel for primaryo2 sensor ;) )causing the ecu to go into open loop mode, causing the car to throw in more fuel to keep things safe. throwing more fuel and possibly not burning all of it may increase the the amount of N2, CO2, CO, other hydrocarbons, blah blah blah. basically the cat has to work harder meaning there is not enough stuff in the cat to keep up with the pace.

im getting tired of typing, so ill make it short.

there is a reason why your cat is gone.

not storing enough o2

the cat does not store o2. o2 is part of the product of the conversion process in the cat. the o2 sensor just reads it.

ill make it simple for you.

reset the ecu. if the cel comes back as catalyst effeciency and secondary o2, then they are both gone.

youwant to physically check the cat and o2 sensor? drop out the cat and look through it. if you can barely see anything or nothing at all, then it is gone.



this isnt your high school science lab. simplicity = go get a cheap and simple voltage and continuity meter from walmart, kmart, walgreens, or riteaid. measure and compare to specs.



actually, there are many reasons as to why the cat will go bad and get clogged. i believe whatyou are trying to say here is that the primary o2 sensor can go bad and throw a cel (problem here is, there is no cel for primaryo2 sensor ;) )causing the ecu to go into open loop mode, causing the car to throw in more fuel to keep things safe. throwing more fuel and possibly not burning all of it may increase the the amount of N2, CO2, CO, other hydrocarbons, blah blah blah. basically the cat has to work harder meaning there is not enough stuff in the cat to keep up with the pace.

im getting tired of typing, so ill make it short.

there is a reason why your cat is gone.



the cat does not store o2. o2 is part of the product of the conversion process in the cat. the o2 sensor just reads it.

Not to argue but the o2 voltage fluxuates to fast for a "normal" DVOM
So you will not get the readings/spec's you are looking for.

And, o2 is stored in the cat just for a little bit. For a correctly working cat to work, and last it needs to switch between rich and lean. lean to store o2 to burn when rich. I admit I don't know what codes are for what for your car. Is there really a code for the cat? and if there is it is set from the downstream o2 sensor.

That is just how it should work.

SH

Yeah I didn't know there was really a code for the cat either, until I looked it up for this thread. It's the "Catalyst System Efficiency Below Threshold" code (I believe).

Ok, I've had the cat replaced so I'm trying to buy the O2 sensor fast. Im just looking for the cheapest thing but I'm not sure what that'll be. I see bosch, denso and no-name on E-bay. Wondering if someone could give me a link to something, I have a 98 civic EX. Sorry for all the trouble guys but thanks for helpin me out.

Ok, I've had the cat replaced so I'm trying to buy the O2 sensor fast. Im just looking for the cheapest thing but I'm not sure what that'll be. I see bosch, denso and no-name on E-bay. Wondering if someone could give me a link to something, I have a 98 civic EX. Sorry for all the trouble guys but thanks for helpin me out.

I would say, stick with a name brand. I've heard of O2 sensors working for a week then dying.

Be careful not to drop it either.

SH

ebay universal denso 4 wire off ebay for $35. still working for 2+ years.

OK. Got it superblue. Last problem, do you remember what wires were which on the OEM plug? This one came with a chart saying this color goes to that color ect, but I cant see how it can be the same for all cars. I guess I need to know the ground, heater power 1 & 2?, and signal wires.

dont remember. this is 4 wire? what does instruction say? color on new sensor? colors on old harness?

yeah this is a 4 wire denso. The colors on it are, black, black, white, and blue. I havent taken the old one off yet.

OK. Got it superblue. Last problem, do you remember what wires were which on the OEM plug? This one came with a chart saying this color goes to that color ect, but I cant see how it can be the same for all cars. I guess I need to know the ground, heater power 1 & 2?, and signal wires.

You have two grounds, one power and one signal
Two black
one yellow or red=heater+
one white=signal

Get out the voltmeter Yellow should be 12v. with key on. White should be 0v

SH

the two blacks are ground and its polarity does not matter with the old harness. there should be a power and signal. match those two with the old harness. the denso instructions should identify those.

Ok sounds easy enough. Just looked around the sensor before and it didn't look like you can get the whole thing out including the pigtail connector because it goes up through a small whole in the underbody. Did you just use the small amount of wire under the car to connect the new O2? It would be easier to get the whole thing out, if you did it that way, how? thanks.

guess not..

you can just make start splicing wires right under the car, or, you can yank on the harness until the junction plug comes out.

Oh man... back. I finally got around to doing this, eveything went fine until I had to crimp the wires together at the end. When I was stripping the coating off the wires hanging out of the underbody one of the wires fell out. So that must mean it pulled right out of the pin connector, great. I was thinking that might happen so I was trying to hold the wire steady the whole time but it just came out. So is it hopeless now? even if I found wherever the pin connector is, how could I put a wire back into it..

just go back up the wire and solder them back on color matching the original wires. if not, you can always rewire from the ecu back down.

ok, but I dont know where the wires go up into the car. It looks like its just behind the firewall or something, how do I get to the location. Or are you saying the wires go straight to the ecu, because the wire that came out was only about 5in. long.

Yeah, I still cant find the hole the wires come through inside the car. I tore up the whole area around the upper console but I don't see any hole in the floor, is it even able to be reached?

OK, I found the hole, rewired everythings in place. I thought there would be a short because I was driving for a while without the wires connected. So a code did come up, 65 short in circuit of secondary O2 sensor. My owners manual doesnt have a location for the fuse. Can somebody tell me which one it is? That is what the short is linked to right? By the way the wires on the old one were blue white black black, the new one was green white black black. I connected the whites, blacks and then the blue to the green, hope theres no problem with that.

rewire it up and reset the ecu. also, check your other post.

Alright, looks like I have to go back under there. But first, how do you reset the ecu, I never did that.

pull the negative cable off the battery for 10 secs then put it back on. cel is reseted.

Well, I reset and the light came back on so the code wasnt stuck in there. I bought a voltmeter and tested the volts on the ecu side of the O2 connector. The wires on that side are; white with a red stripe, green with a white stripe, black with brown dots and black with silver dots. Oddly, the only reading with the key on came out of the black with brown dots. Even stranger, the other side on the O2 connector that connects to that wire is one of the black wires. So thats definitely something wrong then right. We thought those black wires were grounds but one isn't and on the O2 side they are both flat black, cant distinguish between them. So on the O2 side green goes to green, white goes to white, one black to the black with silver and the other black to the black with brown. Now how do I distinguish between those colors connecting to the new O2 sensor. I have the old O2 and can match up the wires as to how they go around the connection to the O2 but its impossible to tell between the two blacks. Also, when I tried to read the ohms I didnt get anything, and I saw it says it cant read under 100 ohms in the instruction book. What am I going to do!?

what year make and model is this car? assuming this is the original engine using the original harnesses..

1998 honda civic EX.

O, and I can't even begin to explain how Im thinking this, but the only thing I think I need to do is switch the two black wires. Just puttin it out there.

Well, I reset and the light came back on so the code wasnt stuck in there. I bought a voltmeter and tested the volts on the ecu side of the O2 connector. The wires on that side are; white with a red stripe, green with a white stripe, black with brown dots and black with silver dots. Oddly, the only reading with the key on came out of the black with brown dots. Even stranger, the other side on the O2 connector that connects to that wire is one of the black wires. So thats definitely something wrong then right. We thought those black wires were grounds but one isn't and on the O2 side they are both flat black, cant distinguish between them. So on the O2 side green goes to green, white goes to white, one black to the black with silver and the other black to the black with brown. Now how do I distinguish between those colors connecting to the new O2 sensor. I have the old O2 and can match up the wires as to how they go around the connection to the O2 but its impossible to tell between the two blacks. Also, when I tried to read the ohms I didnt get anything, and I saw it says it cant read under 100 ohms in the instruction book. What am I going to do!?

Hmmm?? Why can't they follow color codes on these parts. It makes it hard on all of us.

You have voltage on one of the black wires?? Take your DVOM and check for continuity on all wires. use the diode setting and connect the ground of the dvom to a chassis ground. Then pinout the connector from the car. with the key off. You should have two wires that have continuity those are grounds. Then you should have one wire with 12v with the key on, and the other should be the signal from the 02. That covers the car side.

On the o2 check for continuity through one black wire and the green, I believe the heater side of the o2. Both black might have continuity with the green. once you have continuity now check for ohms. The wires with ohms/resistance are the heater wires.

If you can get this far you should be able to figure it out from there.
If not give us the answers and we will get you through this mess.

SH

This is just not working out. Im going to buy this Walker O2 that has a pin connector on it made for the car. Ever hear of walker? 160$...

Also, still does anyone know if theres a fuse for the secondary O2 sensor?

This just came to me now but when I bought a "universal denso O2 sensor" I dont remember it specifying if it was the main or secondary. Or does universal mean both? I mean it fits and all but..

the o2 sensor can be hooked up as the primary or secondary.

this thread is getting outrageous. i mean, i just never ran into someone who has had this much problems with an o2 sensor install. its ok, we will still help ;) i got lost in all the wring descriptions, because, some of the wiring colors you described dont exist on a 98 ex. i think the wires may be discolored or you are looking at them with low lighting. i remembered the denso instructions were really easy to follow. assuming the wiring was never hacked before, you should just match up the colors and solder.

anyways,

3 of the secondary o2 sensors wires run directly to the ecu. 1 wire shares a ground with a relay. i dont really remember exactly off the top of my head which relay it is, because, there are just too many wiring diagrams for one person to remember.

download this helms for wiring specifics.

http://forums.clubsi.com/showflat.php?Cat=0&Number=5045087&an=0&page=0

it should help you clear up alot of questions you have.

just find the o2 sensor wiring diagram and match it to the ecu pin diagrams for the 96-98 civics. that will give you a clear picture of how it runs.

Wow, that helms really did the trick. Looks like I only had the signal ground and signal mixed up, I switched them and everything looks fine. Thanks for all the help and not givin up on me. Now I can officially end this post! :p

:banghead: Spoke too soon :banghead: These wires have to be connected correctly now. I know the heater wires, the signal wire, the other must be the ground, have them all connected. I checked the fuse, its fine. I think this O2 is bad, can you tell me exactly how to check if it is? You said something about 10-40 ohms? between what two wires? My friend has a good meter but we dont know how to use it. :banghead:

:banghead: Spoke too soon :banghead: These wires have to be connected correctly now. I know the heater wires, the signal wire, the other must be the ground, have them all connected. I checked the fuse, its fine. I think this O2 is bad, can you tell me exactly how to check if it is? You said something about 10-40 ohms? between what two wires? My friend has a good meter but we dont know how to use it. :banghead:

The ohm's reading is for the heater side of the 02 sensor.
If it is a good meter you can check voltage on the signal wire.
Set your meter on 2v. The reading should flux-u-ate between 0 and 1v
However very fast 8 - 10 times a second. Here is where you need a good meter, you need to look at the average of this voltage this should be between .4v to .6v if the sensor is good/warmed up and the car is in fuel control.

You almost need a scope to check this accurately however this should show if you are in the ballpark. Go A's

SH Sorry about flux-u-ate Brain isn't woke up!