The Dreaded P0420 Code
 

The Teg threw a random code while driving today -- P0420 (unexpected oxy sensor readings, bad cat, etc.)

It hasn't popped back up, but I'm starting to worry if the cat is going bad. Not a cheap fix... 140K miles -- is this a reasonable amount of time (what's the average?) Could be a sensor...

Hopefully it was an EOC fluke (crosses fingers).

RH77

O2 sensors are easy to replace and a cat isn't too hard to replace either.

OBD-II Trouble Code: P0420 Catalyst System Efficiency Below Threshold (Bank 1)

That's a great site -- they cover some obscure codes that saved me in the past.

I couldn't consciously run it with a bad cat or sensors, so I'd have to fix it should it become a continuous problem. The goal of retaining the car is a combination of environmental and economical reasons, so those two factors sometimes don't agree.

Nevertheless, it would be a great time to replace the whole rattling exhaust system. :thumbup:

We'll see if the code returns...

-Rick

Hopefully it's just a fluke. Crazy computers

I'm in the same boat with the Insight. Don't bother with any of the tricks on torching the rear O2 to see if its bad just replace it.

It is said that cats don't go bad, but just get caked up with sulfur. One trick I heard about but haven't tried yet is to pull the cat, dunk it in a lemon juice solution and bake it for a good 6-8hours

i have had that code for years, no emissions testing = no cat :)

If the exhaust rattles, the cat melted down and is throwing the code since it's not cleaning the exhaust like it's designed to. I removed my cat for performance reasons and simply tied my 02 sensor (downstream) to the frame and it keeps the light out.

The major rattle/buzz is coming from an inner-tube style A-pipe that busted loose years ago (very common Honda flaw). I pulled the heat shields as well -- all they did was rattle.

Something else further back is rattling -- likely the muffler. The 3rd random clanking occurs at low RPM idle -- the source can't be ID'd. It's a loud metal-to-metal clank/squeak.

I used a data logger to check the pre- and post-cat O2 sensors and compared the output to an expected voltage chart (about a year ago). It all was well, yet the rattles haven't changed.

What's the average service life on the converters? The car won't pass inspection without one (which is coming up -- plus I wouldn't feel comfortable with the emissions factor)...

-Rick

I've been told the cat life is about 100k. My exaust was making a weird noise and I went to the shop. They told me I had a crack in my manifold just from the test drive. They came back, took off the shield and showed me a huge crack with exaust coming out of my manifold. A new sound started a couple of months later and they narrowed it down to a heat shield. They told me just keep it there and don't worry about it.

If you have an angle grinder and are pretty handy you can replace the cat yourself, most parts stores will have a direct fit replacement unit available. I changed one on my mom's Camry. Exhaust work basically involves grinding off some rusted bolts and slapping the new piece in. Usually.

So far, the code hasn't returned. I recall something like this happening a year or so ago. The ECU probably got confused with the EOC-ing during warmup...

So you EOC with an auto? I'm too worried about transmission internals to try it personally. How long have you being doing it?

Nearly 3 years (probably over about 35,000 miles -- 140K total on the odo). Probably about 3-5% of the tank is EOC -- I don't do it really often.

I have concerns of the transmission, but so far so good. I modified the kickdown cable to increase the fluid pressure during shifts (to avoid slippage, engage the TC sooner, and hopefully extend the life during normal operation). Other techniques like rev-matching and throttle-lift shifts hopefully help.

I'm also converting to a fully synthetic fluid (draining the pan, and refilling). This weekend will be the second installment -- I haven't fully flushed the works, so there is some residual ATF still in there. The condition is light red, no shavings, no burnt smell.

When it finally does go, I'll likely look for a 5-speed to swap.

As far as other models, it's a toss-up. If it's rated to be towed behind an RV, then it should be fine. Otherwise, it can be considered a risk. For reference, I've heard of a few late-model Escort Autos failing in the low 100K's (a couple ZX2's and a 4-door). It could have been related to abuse or lack of maintenance.

-Rick

Just got a P0420 code a couple of days ago and my FE has plummeted to ~33mpg. My gut tells me that it is the O2 sensor ahead of the cat; I figure that one would be used to trim the fuel air mix. Any thoughts?

It is most likely your cat. The front O2 sensor likely wouldn't have anything to do with this code being set. The rear O2 being bad could cause this, however since your FE has fallen off significantly as well that would seem to suggest a plugged cat.

I have to agree. The P0420 code is a cat monitor code related to the rear (downstream) O2 sensor.

huh...
 

It cleared up on its own. Whatever... and I'm back to getting my good mileage again.

The code came back again. Mileage has been so-so, but with the warmer weather, it's hard to say. So I went and replaced that cat around the middle of February. Since then, it seems like my mileage seems to get better as the car warms up, just like you'd expect, then peaks and tails off again. Then, just the other day, the code popped up again... any thoughts?

maybe a bit OT, but isn't a catalyst supposed to remain unchanged while helping chemical reactions? So technically the cat should not 'change' over time except for soot deposits if any, if at all... So what would 'age' the cat to require a replacement? Can't it be cleaned up and re-assembled in place, like could be done once upon a time?

Lots of other factors