Fishprod

Hi I'm new, and looking for help. Or advice really. I have a 98 Civic ex. The other day my exhaust broke AGAIN. It just keeps breaking at connection points. I normally would just take it to the shop and pay them to put the new part on.
Anyways, I was just driving and my car gets all loud and I knew it broke on another older part of the system. I looked under to see if anything was hanging and it wasn't so I just figured I would wait till my day off and check it out then.
The next day on the way to work in my loud *** civic when my check engine light goes on. So I turned around and went home for a different car.
I got it scanned the next day and got a PO420. It was THE ONLY CODE. I then cleared it. It stayed off most of the day while I was in town. On the way home on the interstate, I was going 70 mph most of the way but then I sped up to 75 mph and the light came on again.
I checked out my exhaust thoroughly when I got home. I noticed a rusted hole/crack forming at the narrowest part of the pipe coming off of the cat. Right after the main connection to the cat.
I figured that when I started going faster, more outside air started coming in the hole and triggered the sensor that is just right there in the cat. I cut the pipe a couple inches down from the hole and the other part just kinda finished falling apart. everything looks fine from the engine to the cat. the cat is rusty but looks fine, no holes or anything. I looked into the back of the cat thru the hole I cut in the pipe and it's all white and clean looking. o2 sensor looks as good as new...looks...
I used some converter pieces and put the pipe back together. I slid a piece into the connection to the cat. It doesn't stick in far enough to touch the sensor or the material inside the cat. It's sealed very well now. Almost as quite as it was before the recent break. The car runs the same as it ever has.

My question:

The check engine light was still on when I did the repair. I drove it almost 70 miles today. never got loud, fix holding up well. The check engine light it still on and I am assuming it is just still storing it from memory. I imagine when I get it cleared it will stay gone unless ..coincidentally..the o2 sensor broke at the same time as the pipe, or the cat broke at the same time... which I doubt. I clearly got a PO420 the first time.
THEN, I found things on websites saying that if a secondary o2 sensor is reporting a code of any kind besides the sensor itself, after repairing the problem the check engine light should automatically turn off.

Is that true?

Or do I have to clear it.

It seems to me that the pipe crack right next to the sensor would most likely be the issue. What do you guys think?

Thanks!

BlackDeuceCoupe

AFAIK, anytime you get a ODB2 CEL, that's emissions related, it will not clear itself automatically. ODB1 used to do that, but not ODB2. But, don't take that as gospel.

I've been getting a P0420 code, occasionally, every since I puked a dizzy, and blew out my CAT.

LoL! What I do is carry a Equus 3030 Innova scanner (best invention since water) in my glovebox. When I trigger a P0420 CEL, I simply clear the code. Then, I'm good for a few more days.

I think I have a leak in the gasket area, on the CAT inlet. As soon as the weather cools down (here in Arizona), I'm going to install a new gasket. In the meantime, I'm having fun playing with my scanner.

BTW, this code won't hurt anything, as long as you aren't running too rich. You aren't running off the maps (limp mode). It's just a PITA having that CEL staring you in the face (ahem) which is the whole idea. It's *supposed* to bug you, until you fix the problem...

Fishprod

Thanks for confirming that for me! I Cleared my code now after the fix, took the car up to 85 mph and no code! So far I was right! it wasn't the cat!

Thanks!!!

BlackDeuceCoupe

So far, so good...

It might come back, though.

On my ride, after I clear the code, it takes 3-4 cycles for the evap & cat sensors to complete their tests. All the other sensors complete testing as soon as you start your car the 1st time, after clearing the code(s).

By 'cycles', I mean start your car, get everything to operating temps, drive for x number of miles, turn off your car, let the temps drop to x degrees.

In my situation, it takes a day or two for the evap & cat sensors to complete testing. I start my car and drive to work (1 cycle). After work, I drive home (cycle 2). Next day -- same thing (cycle 3 & 4). The evap always tests fine, but the cat is a crapshoot.

And, I'm not imagining this. LoL! I can see the evap & cat sensors in test mode, for a couple of days, after I clear the code with my scanner.

Sometimes, my P0420 code will stay away for several days. I've read that the cat readings have to fail on 2 consecutive cycles, for the CEL to light up.

Anyway, wait and see if it comes back...

BlackDeuceCoupe

BTW, when the weather gets cooler, and I drop my cat and install a new inlet gasket, I'm going to do the ol' "foul adapter" trick.

Let me see if I can find an example...

Here you go: https://honda-tech.com/tags.php?tag=fouler

Take your pick!

Here's one with purdy pics: https://honda-tech.com/forums/acura-integra-type-r-8/spark-plug-non-fouler-1841240/

Fishprod

So light came back on today. same code. Don't really know what to ****in' do. I can't afford this ****! The connection from the manifold to the to the cat is so rusted I'm sure no one will be able to remove the cat from it without it breaking. Even if they do I'm sure it will just break this winter. same goes with the pipe after the cat.
Whats with this odb2 ****? Is it some kind of conspiracy? Because we HAVE to have this part they can charge whatever they want for it? I know, valuable metals, whatever.

Emissions is bullshit. If the gov was really concerned with the environment, our cars wouldn't even use gas and all the topics here would be "my solar panel is bla bla bla..." or "I plugged in my car last night and it didn't charge" or "can I use lake water in my hydrogen civic?"

FML!