Hawks88

Hello my name is chaz and i am a new member here. Since i can't get any direct answers for my 99 honda civic lx i was told to come here. I had a broken tail pipe on my exhaust. before i got it replaced everything on my car was fine and dandy. I had the exhaust pipes and muffler replaced so i can pass emissions test. this was done last saturday. today is wednesday and my check engine light came on. P0705, P0174, P0174, P0170, P0420, P0171 are the codes that came up. My car is running fine i dont notice anything different. i know what the codes mean after i looked them up. I went back to the shop where i got my exhaust done and basically blew my off. I asked someone and they told me since you got new exhaust pipes and a muffler check your o2 sensors and make sure they are plugged in, which i did and they are. He then told me to try and reset the battery because it probably wasnt done at the shop. I have not done that yet and thought i would come here and see what you guys think i should do.

TomCat39

Resetting ECU (usually by pulling back up fuse for 15 seconds or so) is always a good place to start. Then pull the codes if any return.

Unplugging the battery for 30 seconds will also reset the ecu but I don't know if you then need to get your radio code again or if you have to do anything when hooking up the battery for the car alarm etc.

If you have an obd2 scanner you can also use them to reset all the codes to see if they return.

Hawks88

Thanks TomCat for the fast reply. I am still trying to figure why those codes popped up after my exhaust pipes and muffler were replaced. I am very persistent on keeping up the maintenance on my car. I use exactly what the manual tells me to use. One guy told me maybe the new exhaust stuff threw off the readings since its a aftermarket exhaust system with bigger pipes. The cat is still on there. Here in Seattle you have to have a cat on to pass emissions testing. I did notice my car has more power and torque its like night and day difference. Its just hard for me to believe that the cat and o2 sensors went bad after putting in a new exhaust system and before it was done everything was fine no codes no nothing.

TomCat39

What the person told you is quite likely. The ECU stores running information and when things change significantly from the running values, it tends to throw codes. With the better flowing exhaust, that impacts idle, fuel trim at idle and even the downstream O2 readings will jump significantly in value.

Your basic step when changing anything, i.e. intake, exhaust etc., is to let the ECU "relearn" your new setup.

It's also why in general diagnostics, when a code is thrown, the first thing you do is reset the ECU and see if the code returns. If it returns then it's considered a legitimate code.

Hawks88

I am going to reset the ECU by unplugging the 7.5 fuse under the hood in the fuse box. I know there is a few 7.5 fuses there but one of them is for the battery and that's the one I'm going to pull. The Honda guy told to pull it and wait a good 5-15 min before plugging it back in. He said don't pull it and plug it back in immediately give it a few min.

TomCat39

Yep, that would be the back up fuse, the exact one to pull and wait a few minutes and plug back in. That is the proper reset procedure.

Hopefully you get no returning codes.

Hawks88

i will let you know how it goes. i hope i dont get returning codes. i had no codes before so by resetting everything it should be fine.

JRCivic1

Sometimes welding near O2 sensors damages them internally. If the exhaust shop did any welding near where the O2 sensors are mounted, and they were not removed, it is entirely possible that they were damaged during your exhaust installation.

Hawks88

That did cross my mind. they did do a little welding from what they told me. nothing extreme from what the tech said. i just reset my ecu and i will see how this goes.

TomCat39

Best of luck!

Hawks88

well tom i passed my emissions test here in seattle. i was really nervous. i was watching all kinds of youtube videos on what to do when resetting the ecu to pass emissions test. some of those videos they were driving these weird routes doing weird things to there cars. they were saying that you have to do these things because if you dont you will fail emissions. i was thinking why dont they just drive there cars for a few days before getting tested. thats what i did. i just drove my normal route to and from work running errands etc... so far no check engine light. its been 3 days.

TomCat39

Awesome, glad it all worked out just by resetting the ecu and letting it relearn.

Much cheaper than having to replace the o2 sensors.

Hawks88

what is the cable or whatever the hook up to peoples cars during emissions test's. i forgot to ask the tech. i was sweating bullets thinking i was going to fail. someone told me its a data cable to check certain things on cars to ensure no bad stuff is entering the air.

TomCat39

It's the OBD diagnostic port they hook up to. OBD stands for On Board Diagnostic if I recall correctly.

Hawks88

Oh ok. Well my check engine light turned back on. That's means I have a problem. I have not had it checked yet but I will in the next few days. I going to drive around Etc.. to see if goes away. It has to be something with the exhaust I never had a problem before I had this new one installed. My car runs fine I don't notice anything different. I've also heard putting after market parts on hondas cause issues. Don't know if that's true or not.

hawks85

well tomcat my check engine was coming and turning off the last few weeks. All the codes that popped up on my first thread about this disappeared except one. p0420 i think, it means my cat isnt operating normal. i dont understand its brand new. i checked the o2 sensors made sure everything is nice and tight under there after my entire exhaust system was replaced. im glad this happened after i passed my emissions test. i am not buying another cat there fricking expensive. i took it back to the shop and they found nothing wrong so now i am confused. my car is running fine nothing seems to be wrong. i am going to try and find a cat cleaner maybe something is in there i dont know. someone told i can remove the cat and soak it in cleaner overnight or something like that. i said maybe but it makes no sense because its brand new.

TomCat39

Why the second account?

And it's probably not the cat, I wouldn't go messing with that. It's more likely the 2nd o2 sensor or the wiring between it and the ecu.

BigPapaBear

I would wager that your exhaust increased the air flow through your engine (hence the power increase) and you're getting codes because the ecu isn't tuned for that (needs more fuel and is running lean). Since it would cost you a lot to tune it, it's probably best to have someone create a restrictor for the exhuast, so your air-fuel ratios are back at an acceptable range that the ecu can handle. You also don't want to damage the engine because it's being run lean, so I'd be careful running the car hard.

That's my educated opinion anyway.

hawks85

well i was curious so i got up under my car like i was up in there looking your right tomcat my second o2 sensor wasnt screwed in all the way. when i checked the first time i just touched everything. the second o2 sensor i unscrewed with my bare hands no gloves or wrenches.it was easy no pressure using my hands. maybe that was the problem only time will tell. i took it out and looked at it to make sure it was not damaged. i put it back in and i screwed it in nice and tight reset my battery. do i really have to get my car tuned to my exhaust so my ecu reads it properly? i mean the pipes are bigger but it still fits where the original pipes were perfectly. if i get it tuned how does it get tuned? is this something i can do?

BigPapaBear

No sorry. I think you found your problem.

eghatch9295

iTrader: (1)

a loosely threaded secondary o2 will not throw a code. google spark plug non fouler trick, follow the instructions. code will not come back, no ecu messing with fuel trims. etc due to the code.

TomCat39

If air can get in around the O2 sensor and reduce the emission sensing why would that not throw a code?

I realize the downstream doesn't have anything to do with fuel trim but I would think that the code would appear weather it's high or low from a set range of expected readings. Loose extra air would likely fall low of that range would it not?

BigPapaBear

I could be wrong, but I think there is a vacuum created as the air passes by the sensor, similar to the vacuum a car creates behind it when driving at a high speed. If the sensor isn't plugged in tight, that vacuum could suck air in around the back part of the sensor?

eghatch9295

iTrader: (1)

nopers. we used to hide them up with zip ties to pass emissions. my fiance's 00 LX threw a p0420 code 2.5 years ago. i did the non fouler trick to get it to pass emissions, light still has not come back on, and i have no symptoms of a bad converter. letting the sensor just hang there would provide the same result, but the emissions tech would probably notice it on this engine.

eghatch9295

iTrader: (1)

on a wideband, maybe... on a primary reading, probably, these sensors aren't programmed that "smart".