Master Bill Flex

Last Fall, i got the dreaded P0420. After doing some research, ive come to the conclusion that it could be either an exhaust leak, bad o2 sensor, or a bad cat. I havent done anything about it yet, but that winter, i noticed that a loud rattling sound would come from underneath the car. It sounded like it was coming from the cat. The noise seemed to get louder depending on how cold the car was. As the car warmed up, the noise disappeared. So of course, i looked into it a little bit and found that some people either removed the heat shield or tightened it with a hose clamp in order to shut it up. So i did, and it shut it up. It was actually MUCH quieter while driving.

Now that inspection time is coming up, i wanted to look more into the P0420. I recently discovered something relating to the rattling noise. Evidently, a cat rattles if it is bad. Since it doesnt rattle anymore, should i worry about the cat? Typically when cats go bad, dont they smell/rattle/glow? Im fairly certain that i dont have any exhaust leaks, the car is wickedly quiet, sometimes its hard to tell when its on. Do 02 sensors typically go bad on the 2.3 cl's? what about cats? I heard that i could do a vaccuum test to check if the cat were bad, any thoughts?

So here is my order of attack:
1) Check cat with a test of some sort, something cheap
2)if cats good, replace o2 sensor (front)
3)if still getting code, check for cracks/leaks

any thoughts? any input would be greatly appreciated!

AznX TL

i've went thru 2 o2 sensors since ive bought the car 2 yrs ago.
if the cat was bad you would get a cel for it. the rear o2 sensor would be the one that goes if the cat is bad.

Master Bill Flex

and another thing... seafoam in my gas tank temporarily gets rid of the p0420, but only for about 200 miles or so. would anyone think that its maybe cleaning or helping the 02 sensor?

Master Bill Flex

i think i found the problem

when i give it gas, for the first 2k rpms, i can hear a very faint "put-put" coming from what seems to be the cat... or maybe right after. after reving over 2k, i cant hear it anymore.

so i assume this is the problem, now do i have to replace the enitre exhaust? could i just send it to some muffler place to get it patched? i noticed that the exhaust is in many pieces, would i just have to get one piece replaced?

any help would be praised , ive got my inspection due next month and i need to get this fixed asap.

Master Bill Flex

aight, so evidently i had a rusted bolt right after my cat. got it fixed for free at Cole muffler, no more noise.

...but i still have the p0420

since the scanner says "(bank 1)", does that mean its receiving the error from the first 02 sensor?

Shotgun3131

Im getting the same code on My 99. You get any head way with yours?

TexasHonda

P0420 is set when the ECU detects poor performance from the catalytic converter. Specifically, the rear O2 sensor shows a voltage pattern similar to the forward O2 sensor, when it should have a steady, slow voltage change pattern. I had this symptom on another car and monitored rear O2 sensor voltage for some time w/ my OBD2 scanner before replacing the converter to remedy the problem.

Note, it can be caused by bad forward or rear O2 sensor, leak in exhaust system upstream of catalytic converter; crack, gasket leak, etc, or failed catalytic converter. If converter rattles when you shake it (if you can), the converter is bad. The converter I removed (Subaru) looked perfect but was no good. I replaced w/ an Eastern Catalytic converter which has worked fine for a couple of years now. A Honda converter is very pricey, last I checked so make sure that's the problem before replacing converter.

good luck

bRunCL

iTrader: (1)

I was in the same situation. I replaced the cat with an aftermarket one and the P0420 code came right back. I've had the car checked for exhaust leaks and several shops have assured me that i dont have any. My next step is to try a new rear o2 sensor. If that doesnt work i'm going to use a o2 spacer to hopefully eliminate the code and the damn light.

TexasHonda

P0420 can be a difficult code to resolve. Monitoring w/ a scanner may provide some additional insight, whether voltage signal is constantly tracking forward O2 sensor, occasionally working correctly (slow voltage changes in rane 0.2-0.9V), or completely off (flat constant signal out of acceptable voltage range). Later would indicate a bad O2 sensor, former usually indicates bad cat or exhaust leak.

I bought my scanner (Harrison OBDScan) and a used portable PC for about $200 and was best investment I ever made. I've used scanner to resolve several problems since besides the P0420, where it was very helpful. In the case of my Subaru, P0420 would be set and if ECU was reset would stay off for weeks or months before returning. When I tracked the rear O2 sensor voltage signal I found the signal was virtually always tracking the forward O2 sensor voltage. After checking carefully for leaks and cracks in exhaust pipe, I replaced the converter w/ Eastern Catalytic converter and problem has not returned for over 2 years.

Note, in some cars there are two catalytic converters; a pre-cat in the exhaust manifold section and a converter downstream. Thankfully my problem was resolved w/ only the one converter replacement.

good luck

Master Bill Flex

After countless hours of searching the internet for a solution, i gave up and put in the sparkplug non-fouler mod (seen here: http://www.energeticforum.com/renewa...n-foulers.html). I was skeptical at first, but so far 600 miles with no CEL. Ive also got a mechanic that can "look the other way." Im not sure if mechanics typically do a visual inspection of the sensors or the exhaust system, but its good to know people since its illegal. Im also using a Bosch sensor, and i think ive read somewhere that they tend to throw the light, even though they are working. I could be wrong, but i swear i read that somewhere on this site.

To all those with the same situation (which happens to be a stubborn p0420), if all else fails, just do the mod listed above (only if you can get away with it). Since it is only on the second 02 sensor, it wont hurt anything.

Shotgun3131

I get a pretty good rattle about 2000 rpms. Im guessing this is a sign the cat is bad. What has anyone replaced theirs with on here?

Master Bill Flex

i had a rattle too, first it was the heat sheild, then it was a pebble in another part of the heat shield. i would hear it at around the same range of rpm's on both occasions too. Sometimes, bad or worn exhaust mounts can cause a rattle.

TexasHonda

Rattle in a catalytic converter is an indicator of bad converter, not while driving, but while manually shaking the exhaust pipe, the converter element is loose and heard rattling inside the housing. Many times a heat shield will get loose due to corrosion of fasteners and cause a resonant rattling sound at a given rpm. This is not a sign of converter failure.

good luck

chewi

I only get that rattle while driving at the 2000 rpm range. my heat shield is already off but there is still that rattling noise. It does go away some times but if i purposely accelerate a bit harder then it will come right back.

my muffler shop assumes its the cat but i worry its something else.

anybody in the same boat? is there a way to get rid of the noise rather than replacing the cat.

should i got back to acura and have it diagnosed?

TexasHonda

My daughter's 2.2CL has a similar rattle under hard acceleration. I've never been able to pin the noise on anything. I thought perhaps the heat shield was resonating. It's not bad and has been there for 100K miles about now.

good luck