Code P0420... who's had it? (1 Viewer)

shocker · May 10, 2005

Since we've got several threads related to other CEL codes in the archives, I figured I'd start one for this.

CEL went on last week. I reset it without checking the code.

Came back on again last night, so I went to a local auto parts store to have them pull the code. P0420, which is a catalyst effeciency below threshold.

For those who care, I guess this code gets thrown throught the following scenerio (stolen from the FSM):

FSM said:
Air fuel ratio feedback compensation keeps the waveform of the oxygen sensor before the catalyst repeatedly changing back and forth from rich to lean.
If the catalyst is functioning normally, the waveform of the oxygen sensor after the catalyst switches back and forth between rich and lean much more slowly than the waveform of the oxygen sensor before the catalyst.
But when both waveforms change at a similar rate, it indicates that catalyst performance has deteriorated.

Haven't had a chance to check the O2 sensors yet, which the FSM recommends before replacing the cats. I've got a few days before I'll have a chance to hook an ohmeter up to them, so I'm left sitting here and wondering. My question is, has anyone had this code before and had it turn out to be just the O2 sensors?

A search on the forum yeilded this thread and this thread, both over two years old and with no resolution.

I've got almost 125K on my 95, and I'm pretty sure the O2 sensors have never been replaced as I bought it with around 70K on it back in '00. I sent an e-mail to Kansas City Converters to inquire about re-built cats just a few minutes ago, and am waiting to hear what they say.

Figured if nothing else, I'll just sail this one alone and post what happens so that anyone with this code in the future will have a loose guideline to follow.

concretejungle · May 10, 2005

Keep me posted on this as i have had the PO420 code within the month and it's the only code my rig has ever thrown. I had an exhaust leak at the flange behind the last cat and just before the downstream O2sensor. I replaced the gasket, reset the code and all has been well for about 3 weeks now.

Is your truck idloling rough?

shocker · May 10, 2005

Never thrown a code before for as long as I've owned it. (4.5 years, 55K miles)

Truck is running perfect. Nice, smooth idle. Accelerates well. No weird noises.

As Kansas doesn't do any smog checks (the extent of their inspection, and it only happens when you first purchase the vehicle, is to glance underneath and see if the cats are there), I'd almost be tempted to just let it go if it turns out to be just the cats. But I don't think I can live with the CEL light on all the time, and I just like to have things all up to spec regardless of need.

wob · May 10, 2005

I had that code for about a year and a half. Whenever it would come on, I pulled out the scanner and reset it. Just got around to replacing the O2 sensors this past weekend. Keeping my fingers crossed that that will do the trick.

I have 110,000 miles on mine, and I'm pretty sure that the old sensors were original.

Lochsa · May 10, 2005

I had this code about 5 months ago. Only CEL that has come on in the 20k or so miles we've had it. Pulled the code, reset the CEL and it hasn't come back. I'm keeping my fingers crossed that it had something to do with the deep snow I had been driving in.

shocker · May 10, 2005

FYI,

I got a reply from Kansas City Converters.

If it ends up being the cats, I can send them in to be rebuilt for $439.30, with one way shipping back to me included.

They also have a line of "new, quality, direct fit, high flow catalytic converters for $477, shipping included."

If I return my existing converters (shipping label provided by them), I could get a check for "up to" $40 in return, making the total cost for the new cats $437.

Any thoughts on just going with the new ones so that I have no down time? I believe cats to be kinda a commodity item, so I'm pretty sure the new ones would be the exact same size and shape as the OEM ones, which would be an issue for me with my Slee sliders.

tenncrusher · May 13, 2005

I have been resetting that code for several years on my 1996 with 157k. Easier and cheaper to reset than to replace the cats. I can go several weeks without resetting, but when I drive at moderate speeds (45-65) for any length of time, the code is usually triggered. I figure it has to do with heat build up. Since the code clearly indicates cats, I have not replaced my O2s since that code has never surfaced. Otherwise, my truck runs great. I have learned to live with it since the "book" repair is replacement of cats.

shocker · May 13, 2005

tenncrusher said:
I have been resetting that code for several years on my 1996 with 157k. Easier and cheaper to reset than to replace the cats. I can go several weeks without resetting, but when I drive at moderate speeds (45-65) for any length of time, the code is usually triggered. I figure it has to do with heat build up. Since the code clearly indicates cats, I have not replaced my O2s since that code has never surfaced. Otherwise, my truck runs great. I have learned to live with it since the "book" repair is replacement of cats.

I don't have my FSM at my work desk right now, but I think it said the trigger is sent after driving 31-40mph for 15 minutes on a warmed up vehicle.

I'll probably check my O2 sensors tomorrow and figure out what I need to do.

landtank · May 13, 2005

shocker said:
I've got almost 125K on my 95

Time for your 2nd tune up, has this been done? If not I'd start there with plugs,pcv w/grommet, rotor, cap, wires and fuel filter.

wob · May 13, 2005

tenncrusher said:
I have been resetting that code for several years on my 1996 with 157k. Easier and cheaper to reset than to replace the cats. I can go several weeks without resetting, but when I drive at moderate speeds (45-65) for any length of time, the code is usually triggered. I figure it has to do with heat build up. Since the code clearly indicates cats, I have not replaced my O2s since that code has never surfaced. Otherwise, my truck runs great. I have learned to live with it since the "book" repair is replacement of cats.

I think the book says check O2's, then check cats for the P0420 code.

shocker · May 13, 2005

landtank said:
Time for your 2nd tune up, has this been done? If not I'd start there with plugs,pcv w/grommet, rotor, cap, wires and fuel filter.

I did all that a little less than two years and 25K miles ago in June 2003.

Other than the CEL coming on Monday night, the thing is running like a top.

wob · May 13, 2005

shocker said:
I did all that a little less than two years and 25K miles ago in June 2003.

Other than the CEL coming on Monday night, the thing is running like a top.

What kind of mileage have you been getting?

shocker · May 13, 2005

wob said:
I think the book says check O2's, then check cats for the P0420 code.

Yes it does. You check the O2 sensors with an ohmmeter, which I will probably do tomorrow sometime.

landtoy80 · May 13, 2005

Have you tried any those "cat cleaners" that you dump in the gas?
If the cat is dirty , then you need to find out what is cousing it to get dirty or you will just get the NEW cat dirty.

Junk · May 14, 2005

I got the P0420 code right after my new exhaust system was put on. There was a slight leak up at the start that was fixed and the code never came back.

tenncrusher · May 16, 2005

If I were to attempt to fix this annoying PO420, I assume that I should start with the O2 sensors and also look to see if I have any leaks.

concretejungle · May 16, 2005

tenncrusher said:
If I were to attempt to fix this annoying PO420, I assume that I should start with the O2 sensors and also look to see if I have any leaks.

I actually would start looking for leaks first, then 02 sensors.

I simply waited until the truck was cool, started it and climbed under holding my hands around joints in the exhaust until i could feel a leak.

alia176 · Jun 16, 2005

concretejungle said:
I actually would start looking for leaks first, then 02 sensors.

I simply waited until the truck was cool, started it and climbed under holding my hands around joints in the exhaust until i could feel a leak.

I think that's sage advice. Mine threw a P420 today and coincidentally, there was a bad leak right at the first flange gasket. It was totally eroded away. The leak is fixed now and I reset the CEL today. Let's see what happens!

Ali

shocker · Jun 17, 2005

Just an update: I reset the CEL on it the day I made this post, and it's never come back on.

I know I may have a slight exhaust leak since there's a little whistle under acceleration, so my money is on that. I still should probably check the O2 sensors, but my free time has been nonexistant lately.

Bob_Garrett · Jun 17, 2005

shocker said:
As Kansas doesn't do any smog checks (the extent of their inspection, and it only happens when you first purchase the vehicle, is to glance underneath and see if the cats are there.

Wow! they actually look under the truck in Wichita? Up here in KC, they just run the VIN and look to see if the truck is stolen, hand you the certificate and you hand them $10.

Bob

Code P0420... who's had it? (1 Viewer)

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