Hey H-T,
Alright a few weeks ago my cel popped on. Car ***** itself going uphill, total loss of power the whole 9. Had the code pulled at AZ, it came up as the primary o2 sensor. Ordered one online from sparkplugs.com, Ive used them before when my secondary had to be replaced. Put the new primary in on friday night, in addition I changed the battery because the old one was getting ready to die. The light popped back on had it pulled again and its still coming up as the primary o2. Wtf? Any ideas whats going on? I guess it could be a faulty o2 sensor but having worked at an auto parts store I didn't see it too often where o2 sensors just came back defective. The primary o2 in the Si is the one IMMEDIATELY before the cat right? Like less than a foot away from where the downpipe connects to the cat? I'm confused as hell as what it could be and its getting ridiculous when 60+ year old people are up my *** because my car lost the little power it had. Any help would be greatly appreciated, thanks h-t.

 

I assume you have an 00 Civic Si. What specific OBD2 CEL code is thrown? Did you reset the ECU and the same code returned?

 

My apologies, yes it is a 00 si. I don't have the specific number on hand, the guy at autozone showed me and the description read the same way. I thought the ECU was reset when the battery was disconnected but upon reading further it looks like that's not enough to actually reset. Do you have any suggestions on properly resetting it? Would it be fair assuming the could be the reason the code popped back on and is still running like crap.

 

Try to reset and see if it comes back, typically I think if you take the negative off for like 10 mins, should reset.

Or just pull the back up fuse for a few minutes.

Or a code reader can reset it maybe parts store can use theirs to reset it for you.

 

You can retrieve the CEL code yourself by jumping the service connector. Click the CEL sticky at the top.

Reset the ECU by removing the 7.5A hood Back Up fuse for at least 3 minutes.

 

Start the car and let it warm up
Turn the car off
Pull the ECU fuse under the hood -or- disconnect the battery
Let it sit for at least 5 minutes
Reconnect the ECU fuse under the hood -or- Reconnect the battery
Start the car again and let it idle for 5 minutes (don't be pressing the gas or listening to the stereo or anything)
Turn the car off
Start it back up and have fun driving.
Or you can leave the ECU alone and it will slowly adjust over 6 months or so.


Is this right?

 

Alright I'll give it a try, thanks!

 

Edited:

 

So far it hasn't come back on yet. I drove for around 15 minutes, seems like its not bogging as much. Thank you for your help.

 

I hope the CEL remains off.

 

Bump. The cell came back on today on the long drive to work. Stopped by pep boys on the way home (never going there again) and had the code pulled. P0172. Could a different problem be giving the primary o2 sensor a rich reading?

 

Have you checked your MAF, your vacuum/lines, and your fuel pressure? P0172 means you're running too rich, which isn't always caused by the O2 sensors.

 

I checked around the vac lines...everything looks good and tight. I haven't checked fuel pressure yet only because I don't have the tools to do so during the week. I'm not sure what I would be checking on the MAF sensor. Just for dirt and such?

 

MAP, not MAF, I'm an idiot. There's plenty of tutorials on how to clean your MAP online. Just because the vacuum lines look ok doesn't mean you don't have a leak. I'm fairly sure Advanced Auto has vacuum and fuel pressure testers you can rent.

 

Do you have a factory exhaust manifold or aftermarket headers?

 

Alright, thanks for your help.

 

Header is stock.

 

If you have the heat shield still on, take it off and see if the header is cracked.

 

I did take it off for an unrelated reason the other day. Checked it for cracks or leaks in it.

 

Another thought, might have a clogged cat.

 

Checked fuel pressure today. 32 psi with vacuum line attached to FPR, 42 without it attached.

Would a clogged cat make a nasty rattling noise at higher rpms?

I'm not sure what to try next...maybe try returning this o2 sensor for another one.


Edit: Checked MAP sensor with a multimeter 2.87v with key "on" .88v at idle

 

clogged cat dont make any noise. it doesnt rattle but it does seem like the car is not pushing enough power. i had that problem on my si too so i went straight pipe for the cat. um from wat ur saying bout the check engine light.... you know u can use the same one that u have on the cat right? that second one is cheaper and it plug and playssss. just that the wires are a lil longer but its cheaper than the regular one that ur suppose to get.

 

I'm not sure what you're talking about...the downstream o2 is way more expensive than the upstream plus they are two different part numbers. I'm not really worried about saving the $50 or so, I'd rather have the right part in there anyway. Either way if its not the o2 sensor thats fault it would irrelevant anyway. Thanks for your input though.

 

Quick note, there was small leak from one of the seals under the spark plug cover studs. It was not seated correctly and was blowing some air out. I reseated it and pulled the back up fuse to reset the ecu. I doubt that was the problem but I did change my spark plugs immediately before changing my o2 sensor so its a possibility. I'll know tomorrow morning because my commute is about 50 miles. :-\ updates to follow

 

CEL came back on on the drive home today...had it pulled again. Now its throwing P0420. WTF?! Kinda gettin lost as to what's going on. Any ideas?