DTC P0420 - No Driveability Issues

bh357 · Post by **bh357** » Thu Oct 27, 2005 10:08 pm

My Vibe (2003, with 97k miles) recently started throwing a CEL. It did it twice in the past month, where it went off within a couple of days. It did it a third time last weekend, and the CEL has stayed on since. I took it to AutoZone, and had them read the code - P0420 "Catalyst System Low Efficiency". No other codes came up, and there are no driveability issues. Fuel economy has not changed.All info I've found points to replacing the cat, but some people have stated that the O2 sensor may be bad. Has anyone else had similar symptoms? What could've killed the cat in less than 100k miles, but not be showing any other DTC codes? How urgently do I need to get this fixed?Thanks.

bud_one · Post by **bud_one** » Thu Oct 27, 2005 10:57 pm

Service flow chart for that code - step one tells you to monitor both oxygen sensors and look for fluctuation.... - make sure the connector on the oxygen sensor after the converter is not loose or has any burnt wires etc....If that's all good then the culprit is the catalytic converter.... that's the bottom line on the flow chart.... Hope this helps some....

ToolGuy · Post by **ToolGuy** » Thu Oct 27, 2005 11:01 pm

I would say replace the cat and O2 sensors. Cats upward to or in the 100K range usually go by then. If you keep that same Cat and it is already somewhat failing, the longer you keep the old one in place, you will have more issues down the road.

jake75 · Post by **jake75** » Fri Oct 28, 2005 12:12 am

Perhaps these emissions components are under a longer warranty - I thought they were in the US.OPPS - I read 97k as 97km and thought it was a Candian car. At 97,000 MILES you are probably on your own.

bh357 · Post by **bh357** » Mon Oct 31, 2005 12:09 am

Just a quick update. On Friday night, the CEL went out. It hasn't come on since, with a few trips on both Sat (2 trips 20min each) and Sun (1 trip 1hr). These trips were mostly highway driving.I guess for now I just need to monitor and see if the light comes on again and stays on for longer durations.

joatmon · Post by **joatmon** » Mon Oct 31, 2005 12:37 am

Quote, originally posted by jake75 Â»Perhaps these emissions components are under a longer warranty - I thought they were in the US.OPPS - I read 97k as 97km and thought it was a Candian car. At 97,000 MILES you are probably on your own.looking at the 2003 US warranty info (PDF link in thread http://forums.genvibe.com/zerothread?id=1010)Quote Â»For 8 years or 80,000 miles, whichever comes first:If the catalytic converter or vehicle (powertrain)control module is found to be defective, GM willrepair or replace it under the Federal EmissionControl Warranty.

Smity · Post by **Smity** » Mon Oct 31, 2005 10:08 am

If it was the the cat it would be constant. Sounds like one of the o2 sensors is starting to get weak.

bh357 · Post by **bh357** » Wed Nov 02, 2005 1:19 am

The D@MN CEL came on again today. I haven't taken it back in to have the code pulled yet.

ToolGuy · Post by **ToolGuy** » Wed Nov 02, 2005 4:55 am

Unfortunately there is no way to test a converter, unless it is glowing red from under your car that would be a sign of needing a new one! You can tap it with a rubber mallet, if your hear stuff moving around in the housing then the converter is falling apart inside and it will only be a matter of time before a piece falls off and clogs the system. Sometimes a failing converter will not set a code, you will just have reduced engine power and it may rattle when engine revs are brought up.If I were you I would just put a new converter on and O2 sensors on and be done with it. Your mileage is high and the convert will not last another 100K. OBDII systems are very sensitive, if the light came back and it is the same code the systems is sensing something is not right even a little bit.

joatmon · Post by **joatmon** » Thu Nov 03, 2005 9:06 am

I'm in the 4:20 club now too, unfortunately the one that isn't any fun.Threw a CEL today, autozone scanner says it's the P0420. Search turned up this thread, and also philndz'a P0420 at http://forums.genvibe.com/zerothread?id=11691, and satur9's P0420 at http://forums.genvibe.com/zerothread?id=7184 unfortunately nobody has ever posted about having a successful fix to this code. I'm at only 93K miles, but that's still beyond the extended emissions component warranty. Anybody had a P0420 and got it fixed, post up what fixed it for you.I won;t get a chance to poke around under the car until this weekend. will check the cat for loose contents, exhaust leak, bad wiring/connections, etc. seems to be covered well in the softcopy matrix service manual, but I don't have the scan tool and am not going to buy one. Now, if I could make one ...

Toolman · Post by **Toolman** » Thu Nov 03, 2005 10:44 am

If it is the O2 sensor that is in the cat, and not the one right out of the exhaust manifold you will not get any driveability issues. As far as I know all this sensor is for is to tell the ECU if the catalytic converter is failing. I had a Talon TSI which I put i downpipe that eliminated the cat, hence eliminating the second o2 sensor. It threw a code until I got a simulator to put in its place, no reduced power or fuel economy, just that annoying light. I would say that either the cat is bad and/or the second o2 is bad. A new o2 is 35 bucks, I would start there.

rmarkw · Post by **rmarkw** » Thu Nov 03, 2005 11:47 am

Autozone just pulled the same code plus another exhaust code this week on my Buick Rendezvous. Turns out my gas cap wasn't seated properly. Why that would trigger an exhaust code, I have no idea. Probably not the case with your car, but maybe worth checking.

joatmon · Post by **joatmon** » Tue Nov 15, 2005 2:36 am

Quote, originally posted by Toolman Â» A new o2 is 35 bucks, I would start there.Didn't check GM, but Toyota wants $150 Autozone wants $70, so I ordered one, and then today on the way in to work I noticed the CEL was off. So, now I need to decide whether to buy the O2 sensor anyway in case the CEL comes back, cancel the order and deal with it if it ever does come back or perhaps figure out your secret source of $35 O2 sensors and stock up.

jcm1029 · Post by **jcm1029** » Fri Nov 18, 2005 1:21 pm

You need to monitor your o2s. Use a graphing scanner, your bank2 sensor should not have the same wave pattern as bank1. If your bank2 sensor mirrors bank1, your cat isn't working.

joatmon · Post by **joatmon** » Sun Nov 27, 2005 1:43 am

Quote, originally posted by joatmon Â»Didn't check GM, but Toyota wants $150 Autozone wants $70, so I ordered one, and then today on the way in to work I noticed the CEL was off. So, now I need to decide whether to buy the O2 sensor anyway in case the CEL comes back, cancel the order and deal with it if it ever does come back or perhaps figure out your secret source of $35 O2 sensors and stock up.wel, the CEL went away on it's own, and I thought I was golden, but then it came back. Disconnected the babttery for a while, reconnected it, and the ight was gone, but came back after about 400 miles. Today I put in a new O2 sensor, the one after the cat, and hopefully the CEL will stay away. Disconnected the battery to reset the light. It was pretty easy to swap. Have to pull up the frontright side of the carpet on the front passsenger side, disconnect the wire, push the grommet through the floor, and then unscrew the sensor from the exhaust pipe. Probably a metric size that's an exact fit, but a 7/8" wrench was a near perfect fit. pused the box end wrench down the wire and over the grommet. Edit 12/6 Been 1000 miles or so since I replaced the O2 sensor, and no return of the CEL. Still keeping my fingers cossed though.

bh357 · Post by **bh357** » Mon Nov 28, 2005 9:21 am

Just a quick update. The CEL has been out for the past couple of weeks now.

joatmon · Post by **joatmon** » Fri Jan 27, 2006 9:31 am

my quick update, yesterday got another CEL, got it code read at Autozone today, P0420, again hmmm, I'm thinking bad kitty

ColonelPanic · Post by **ColonelPanic** » Fri Jan 27, 2006 5:33 pm

Meow! At least you got upwards of 100,000 out of yours. Most of us have them crap out at a quarter to half that mileage. Hope you can clear up you 420 blues soon and cheaply.

bh357 · Post by **bh357** » Fri Jan 27, 2006 9:57 pm

Just a quick update for me. After a brief 1/2 week of CEL Hell in mid December, I have been 420 free.I guess the only thing I can do is see if it comes back, and stays on for more than a week.

joatmon · Post by **joatmon** » Sun Feb 05, 2006 10:25 pm

Yesterday I still had the CEL. Started it up today and no CEL. Will probably come back, but if it doesn't, then I'll be glad I procrastinated on getting some repair done.

RIT · Post by **RIT** » Mon Feb 06, 2006 2:51 am

If you disconnect the battery for 5 minutes, or so, it will clear the code.I got the CEL just after putting in gas from a station with 10% ethonal. It was the 0420 also.

Post by **NSimkins** » Thu Mar 02, 2006 9:58 am

Well, thanks to the ScanGauge, I'm now officially a part of the P0420 club (I'm at about 60,000 miles). The Vibe's been exhibiting the same symptoms as previously stated in this thread, but confirmed today. At least the ScanGuage can remove the CEL for now. I'll probably work to get this fixed this Spring if possible.Anyone have any other updates to their P0420 story?

joatmon · Post by **joatmon** » Thu Mar 02, 2006 10:05 am

no, not really. for now I'm just ignoring it. MPGs are down about 10%, not sure if it's the CEL or winter gas.I think Savoy had these problems, starting at the bottom of http://forums.genvibe.com/zero...age=7 but I can't find where he ever mentioned a fix

Post by **NSimkins** » Thu Mar 02, 2006 10:12 am

I wish it was one of those cut and dry, "you need one of these replaced", plain and simple fixes, but I may have to see if I can take this up to my advantage (as you quoted above):Quote Â»For 8 years or 80,000 miles, whichever comes first:If the catalytic converter or vehicle (powertrain)control module is found to be defective, GM willrepair or replace it under the Federal EmissionControl Warranty.The weather is too messed up right now for me to be working on this myself. I'll keep an eye on this thread, hopefully something surfaces. If I find out anything, I'll be sure to post it up.

joatmon · Post by **joatmon** » Thu Mar 02, 2006 10:17 am

well, unfortunately for me, I crossed 80,000 miles last MayAnybody know if the front and read O2 sensors are the same? I replaced the rear, but if that didn't fix the problem, I could put the old one in front, and see if that has an effect, then if not, I'd feel better about paying for a new cat. Any performance cat converters I ought to be looking at?

zionzr2 · Post by **zionzr2** » Thu Mar 02, 2006 11:27 am

Oh goody I see what i get to look forward too...was anyones cat, thats throwing these codes, already replaced due to the previous Rotten egg ordeal?

cgello · Post by **cgello** » Sat Mar 25, 2006 8:56 am

I have just over 90K miles and the 420 code came up recently. How soon should I have the O2 sensor or C convertor replaced? Is this something that will hurt the car in the long run or is this simply an emissions problem? I have not noticed any change in perfromance or gas mileage.

joatmon · Post by **joatmon** » Wed Mar 29, 2006 9:30 am

Quote, originally posted by cgello Â» Is this something that will hurt the car in the long run or is this simply an emissions problem? I can think of a couple of scenarios. If it is the second O2 sensor, then it would just cause a CEL, but the converter would be converting, and no particular impact other than driving around with a constant CEL will keep you from noticing if something else goes wrong that sets a different CEL code.If it is the converter, it could be not converting well, in which case you'd be putting out more pollution, but have no other particular impact (other than the constant CEL). However, supposedly (at least according to catalytic converter manufacturers) if the converter is having restricted air flow, then prolonged use could cause some damage to the engine. Not sure what, or how, but I guess it's possible.I replaced my converter last weekend, and so far about 450 miles later and still no CEL. Also, the 10% MPGs that it seems I lost over time are back, so I am seeing a benefit there. If it keeps me from wasting 10% in gas, then I'll have to run ~$5000 worth of gas through it before I see a cost benefit. By that time I'll probably need another one. EDIT 4/9/2006 - Been 1500 miles since the cat replcement and still no return of the P0420 CEL. Also, for the four tanks of gas before the replacement, I averaged 34.1 mpg. The four tanks since the replacement average 37.1 ,mpg

marvelo · Post by **marvelo** » Thu Jun 15, 2006 6:04 am

OK - I'm in the same boat. Got the 420, got the news that its the cat, am struggling to discover whether it really is or not.The key point to me seems to be that there's not clear difference in performance since the CEL. Wouldn't there be a degradation in performance if the cat really was crapping out?

joatmon · Post by **joatmon** » Fri Jun 16, 2006 2:41 am

There are at least two ways that the cataltic converter can fail.The first is what I think of as "the pmh013 method". Her catalytic converter(s) became obstructed with goo, and this did cause significant performance degradation, but never did set a CEL.( http://forums.genvibe.com/zerothread?id=8119 and http://forums.genvibe.com/zerothread?id=2894 )The other way is what I think happened to mine, which is that it did not become obstructed,( or if so not enough to cause any noticeable performance issues), but it lost it's ability to convert the exhaust gasses Maybe the catalyst got used up, or maybe some insulating film was deposited on a critical layer of the thing. I don't know. I think my CEL first came on after a very aggressive acceleration.The first O2 sensor is used by the computer to check the exhaust gasses, I think it gets used in setting air/fuel mix. The second O2 is to watch the perrformance of the cat, but I do not think that the second O2 reading is used in setting any of the engine performance parameters. So as long as the resistance downpipe from the first O2 sensor is not affected, the converter isn't going to affect engine performance, even if it lets you pollute like crazy.

RIT · Post by **RIT** » Tue Jul 11, 2006 2:12 am

Has anyone firgured out the exact cause of the P0420 - is it the cat convertor, or which one of the O2 sensors? Can you pinpoint the problem with the Scanguage? I am getting a P420, but don't feel like paying a dealer $75 to tell me that it is an O2 sensor. It would be worth it, if i knew for sure it was the cat convertor, becuase that would be warranteed.THXRit

joatmon · Post by **joatmon** » Thu Jul 13, 2006 5:33 am

Quote, originally posted by RIT Â»Has anyone firgured out the exact cause of the P0420 - is it the cat convertor, or which one of the O2 sensors? Can you pinpoint the problem with the Scanguage? I am getting a P420, but don't feel like paying a dealer $75 to tell me that it is an O2 sensor. It would be worth it, if i knew for sure it was the cat convertor, becuase that would be warranteed.THXRitI have a scanguage, but if it can display the O2 sensor values, I haven't been able to figure out how. For me it was the converter, but I first tried the second O2 sensor, since it was cheaper, and I was already past the 80K converter warranty. Attached some background info (for 1ZZ, 2ZZ pub is effectively identical)

Attached files cip0420.pdf (20.9 KB)

Post by **NSimkins** » Sat Aug 26, 2006 8:55 am

joatmon, how about an update, still running CEL-free?I'm getting the P0402 more and more frequently now... thinking it's near time to get the converter and O2 sensors soon.

joatmon · Post by **joatmon** » Sat Aug 26, 2006 9:49 am

no cel since the cat replacement. Car is running great, good mpgs, no problems. Happy vibing going on here.It's a tough call though, first I replaced the second O2 sensor because it was cheaper that the cat, but it didn't help, so I think that may have been wasted money. I think if I replaced just the cat, I could have saved myself the $ for the O2 sensor. But then again, if I had replaced the cat first and it was the O2 sensor, I'd have been pissed. You're still under the period covered by the extended emissions component warranty, so take that thing in and get it fixed. Should save you some gas, and you'll pollute less too

abyssvibegt03 · Post by **abyssvibegt03** » Wed Sep 06, 2006 11:12 am

To start I have a 2003 Vibe GT with 87k miles. Ok here is the solution you all have been wanting. The P0420 code signals that: A. You may have a misfire. B. You may have a vac problem. C. You may have a bad Cat. or D. You may have oil leaking into your Cat.Solution: Cheapest to most costly: First check your spark plugs. If your car has been feeling sluggish then that could be your problem. Even if they dont look THAT bad...change them. NGK Iridium tip are standard on GT and are the best overall. Check the ignition coils on each next...they should be in good shape, but if you see something wrong replace it. That is the end of the first phase. Start the car and test drive....any CEL? If so here is step two. Replace the O2 sensors down by the Cat. Still a CEL? Next.....take it in to the shop...you most likely need a new cat, but have them check to make sure...you don't want a new one if you don't have to. Remember if the engine has a misfire then is is leaking gas down to the cat and it ignites in the cat...not a good thing. So get those plugs taken care of and check the o2's if needed. In my case I had an on and off CEL for a month and a half....then it stayed on. Replaced the plugs and waalaah.....goodbye CEL.

Zeppo · Post by **Zeppo** » Mon Sep 18, 2006 10:53 am

I thought I would add my 2 cents to this thread. Our '03 Vibe had the MIL come on this past summer after about 110,000 km. I was awaiting a scan tool which I bought from Digimoto before I had someone else look at the problem. With this tool I was able to read the 0420 DTC for "Catalyst Low Efficiency. According my factory service manual, this is triggered when the Heated Oxygen Sensor 2 (HOS2) is as active as Heated Oxygen Sensor 1. It takes 2 drive cycles before Malfunction Indicator Lamp (MIL) illuminates. The MIL will turn off if the condition is no longer present after 3 consectutive drive cycles.The program clearly showed traces of the HOS2 was fluctuating almost as much as HOS1. I checked my Civic's traces for comparision. The HOS2 was stable on this car while the HOS1 fluctuated. No problem here.Because of some bug in the scan tool it's been clearing the DTC codes on the Vibe every time I checked it. The first time it cleared, the condition it came back after a couple of days. The second time it cleared it the MIL was off for about a month. I had to wait until it came back before scheduled an appointment with the dealer.I just had the convertor replaced last Friday. Unfortunately, my scan tool is out of commission for now but as soon as I get it back I will see if the chart recording of the Oxygen sensors are behaving normally.

vibegtcouple · Post by **vibegtcouple** » Thu Sep 28, 2006 8:51 am

i'm a gm tech i was at pontiac in my home town before they close and i have never seen this before other then when i made it up to but on a test pipe in place of my cat if anyone is still have this code going on p0420 i would like to look at on of your cars i live in spring grove pa. or if you do not have any emissions in you state you can get a test pipe and a o2 sim from ebay that is how i keep my light off but back to you that are having trouble with this code if i have the car i can call gm and toyota and find out what is going on with this code . if anyone need help with some thing just let me now i will give you some gm papers and flow charts to work from they are alot better then anyone else i can get you wireing charts to just let now

RIT · Post by **RIT** » Thu Sep 28, 2006 8:29 pm

I changed my spark plugs about 300 miles ago, and the check engine did not come back on YET . I keep my fingers and legs crossed every day. However, i will take you up on the offer for the instruction papers. Can you scan them and e-mail them, or Iwill paypal you $1 to cover the postage. I love to fix things myself.THX

mike7311 · Post by **mike7311** » Thu Feb 08, 2007 12:51 pm

I think it's time to start this thread up again. I popped up the magic 420 the other day. I cleared the code, but I fear it will show it's face again. Should we start a poll to see how many people are experencing this problem...

msmyer · Post by **msmyer** » Sun Feb 18, 2007 12:38 pm

My CEL light has came on for the 3rd time in the past 4 months. The last time they came back with a code of:THERE WAS A CODE STORED OF -P0420 CAT EFFICIENCY LOW BANK 1. REPAIRS ARE REFERRED TO THE DEALER.This was on 1/17/07.

Post by **NSimkins** » Tue May 08, 2007 2:43 am

Update: just got back from the dealer. Since I'm barely still under the 80,000 mile emissions warranty, they ended up replacing the catalytic converter for free (warranty!) I had my doubts, but they gave me no problems so I'm now a proud owner of a new converter!

joatmon · Post by **joatmon** » Tue May 08, 2007 2:47 am

Good deal. See if you get any changes in performance or mpgs.But the real question is if that pesky P0420 will stay gone.

mike7311 · Post by **mike7311** » Thu Aug 09, 2007 11:43 pm

I'm back with the same issues, but more infomation. I notice the only time I get this code is after I run the car with a full load of people. I'm having intermittant drivability issues right before the code comes on; hard idle, sluggishness. I haven't had alot of time to nail this one down. I hoping someone can give me some starting points. I'm figuring I need a converter. After awhile the light goes out so obviously the problem is still intermittant. I'm at 120,000 miles on my vibe gt and I'm still getting 33-34 mpg, all freeway of course. I run nothing but shell premium 91. All the maintance is caught up and everything is clean, no leaks. I have notice since I got the car that on hard launching's it bogs out then goes, does anyone else experence this. I don't mean riding the clutch, just gas and go...

jvibegirl · Post by **jvibegirl** » Sun Nov 18, 2007 10:35 pm

I'm kickin the p0420 recently. It runs a little rough at idle and at take off. I'm going to start with some new plugs considering i haven't replaced them yet and i'm at 107k miles.Anyways have a good replacement for the 2 cats? Dealerships want over $500 for the part which is basically then entire exhaust from what i can tell. What about welding in some aftermarket cats? Has this cleared this code for anyone?

jvibegirl · Post by **jvibegirl** » Fri Nov 23, 2007 11:57 pm

Any body ever just welded in 2 of these: http://cgi.ebay.com/ebaymotors...h=003I'm not sure if the 2 cats on our OEM exhaust system are the same. My only other option is to replace the entire system.The cheapest part i can find is here: http://cgi.ebay.com/ebaymotors...h=011Basically I just want to solve my P0420 code inexpensively.

terrymcfadd · Post by **terrymcfadd** » Sun Jan 04, 2009 5:59 am

bought an '03 with 120M miles, throwing a p0420. Sensor test indicated bad post cat sensor. Replaced with BOSCH sensor - still got the code. Toyota dealer said it was the cat - replaced it(groan) still got the code. I pulled the plugs - they were fried - replaced em - and the CEL is now gone. Suggest any high milers start thier journey down this path by checking thier spark plugs, and replacing if they look burnt (which mine certainly were).

lmhansen · Post by **lmhansen** » Fri May 01, 2009 1:24 am

I got my P0420 half-way to Iowa at Thanksgiving. Dealer said "bad cat, go somewhere else to have it replaced because we'll charge you $1200" ... At least they were honest, unfortunately, everyone else seems to charge about the same.They cleared the code, and it hasn't come back since, so I'm not certain if it was a temporary issue or not(?)Also, I thought there wasn't an O2 sensor behind the cat? Or, is that connected to the exhaust rather than the cat-part? The instructions posted in here for replacing the catalytic converter made no mention of the second O2 sensor on the part, so ...Well, I'll look at replacing the spark plugs and O2 sensors before shelling out the big money for a replacement cat.

joatmon · Post by **joatmon** » Fri May 01, 2009 9:00 am

Quote, originally posted by lmhansen Â»Also, I thought there wasn't an O2 sensor behind the cat? Or, is that connected to the exhaust rather than the cat-part? The instructions posted in here for replacing the catalytic converter made no mention of the second O2 sensor on the part, so ... There are two O2 sensors. The first one is just behid the engine, pretty much in the exhaust manifold. The second one is between the two cat stages (or at least I think there are two cat stages) Anyway, this pic shows where the second O2 sensor goesbut if you've been running CEL free since Thanksgiving, it must have bene something transient. Hope it stays off

lmhansen · Post by **lmhansen** » Fri May 29, 2009 11:47 pm

Quote, originally posted by joatmon Â»but if you've been running CEL free since Thanksgiving, it must have bene something transient. Hope it stays off Nah, it just came back last weekend. Parked the car once I got back and had it checked today. Same code. I had the plugs replaced a couple of weeks ago, so that didn't do much for me. I'll have to consider getting a new cat from Eastern Catalytic, and install it myself ...

csvibe · Post by **csvibe** » Tue Jul 21, 2009 3:16 pm

I had a code 0420 on my 2003 vibe in april 2008. the converter was replaced the code went away and it passed the NY state inspection.Two weeks later the MIL light is back on. The car runs fine and gas mileage is about the same so we drive it until the inspection is due April 2009. I check the codes and it is the 0420 again. I send the car back to my buddy's garage where the converter was replaced last year. He does some research and talks to a friend of his at a Pontiac dealer. They say the mass air flow sensor causes the problem, it gets a little dirty and runs the fuel just a little too rich and fouls the converter and then code 0420 sets. He put a new MAF sensor in and ran the car to clear out the converter, that didn't work so he had to replace the converter (good news his supplier warranteed the year old converter). Bottom line is we have more than 6,000 miles on the new converter and the MAF sensor wirh no codes. Suggestion: Replace MAF while code 0420 is still intermittent and the converter will survive.