The Dreaded P0420 Code

[RH77]

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...

[Formula413]

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

[RH77]

Originally Posted by Formula413

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

[chuckm]

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?

[Formula413]

Originally Posted by chuckm

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.

[Johnny Mullet]

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

[chuckm]

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

[chuckm]

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?

[hummingbird]

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?

[metroschultz]

Originally Posted by hummingbird

maybe a bit OT,
(1)but isn't a catalyst supposed to remain unchanged while helping chemical reactions?
(2)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?
(3)Can't it be cleaned up and re-assembled in place, like could be done once upon a time?

Lots of other factors in these questions.
(1) Yes. However you are putting simple logic on a complex issue.
...The cat remains unchanged as long as;
Your engine is in tune and you don't accidentally add toxic chemicals in the fuel. (!!Lead!!, some cleaners in high dosages, etc.) This will lead to premature failure and an inability to do it's job correctly.
(2) Cats are made with precious metal bonded to a ceramic honeycomb structure. As they get older the metal will degrade and go away. I have seen cats with 200k on them that still worked well though, so all is dependent on the way your car reacts and you drive.
They do not like excessive vibration and really hate it when you drag them into/over speed bumps.
(3) I don't know of any cats you could open and repair. I know of the early GM units you could open and empty. ?!?!?!?!

So to sum up, your cat will last for a good long time provided you keep the engine running well and you don't abuse the cat.

Hope this helps,
S.