[tonylanz]

P0420 - Honda Accord

The check engine line (CEL) came on and we took it to Autozone to get a free code reading. It was P0420, which turned out to be a very popular code for all Honda Accords. We have a 1999 Honda Accord LX with 140K miles. We called several local Honda dealership and received an estimate of $1K to replace the catalytic converter (CV). This has to be done in order for our 1999 Honda Accord LX to pass the State of Texas annual inspection. We took our vehicle to a highly recommended muffler shop and they replaced an after market CV, with the total cost less than $300. It has been a year now and the CEL has not come on and needless to say, our vehicle passed the annual inspection.

I have done quite a bit of research on this P0420 code and there are a lot of good recommendations. I have tried all of the home-remedies and none seems to work for me (ie. add fuel additive chemical into the gas tank, rev up the engine at a lower gear on the
highway, erase the computer code, buy super unleaded gas, replace OS2 sensor, get a tune-up, replace spark plugs wires,
replace with Honda manufactured CV, and etc....)

This has proven to be an easiest method of fixing P0420.

Good Luck !

 

[Fredsvt]

As Princess posted, the first things mentioned need to be checked, but also the car needs to be scanned with a Honda scanner to make sure the car is in proper fuel control, the trims need to be where they should be to ensure the cat can do it's job.

ok, as a short term "fix" buy a can of carb spray cleaner.
remove the intake duct leading to the throttle body.
use your hand to rev the engine and start spraying cleaner into the throttle body.
run nearly the whole can through it. make it run rough, but don't stall it.

Do this outside, the car will emit some horrendous smells and toxic fumes. The cat will begin to heat up severely as it burns up the unburnt carb cleaner and fuel. This usually works on cars that use oil, the engine oil, especially thrifted oils leave deposits on cats that poison them. If the cat's precious metal washcoat has become ineffective or the substrate has broken up, this will do no good.

When done, go out and beat the snot out of the car.

I've had some luck in keeping the P0420 away for a while this way.

I'd say on 99% of the cars once they start setting a P0420 the cat is dead or dying and needs to be replaced. The PCM in all newer cars are very, very good at what they do when it comes to catalyst monitoring. There are some cars that had too tight tolerance for that monitor and needed to be "desensitized" by having a reflash. The gen6 accord isn't one of them, neither is the Ody as far as I know.

Replacing air/fuel and the rear monitor o2 sensor won't do anything. If those sensors have an issue, normally they will set codes themselves for performance issues, i.e. slow response, etc.

 

[rgdewar]

Code Problems

When my Accord Check Engine light came on I changed the O2 sensor on the manifold (109 K). Shortly thereafter the light returned. I then changed the O2sensor on the cat converter and in about 10 days the light went out and has stayed out "knock wood" for the last couple years (134 K). The mileage was somewhat better before I changed the sensors but the performance was better after. I was told that you can sometimes smell the converter when it is going bad. A sulphur smell. Anyone heard of that? Seems likely that changing the sensors, although a bit costly, after 100 K is a common remedy. I uses Bosch after market but still cost about $180.

 

[princess]

sulfur smell does NOT equal bad cat. Most cars will get the smell when the cat heats up....like a long uphill drive.

It IS a problem is the smell is inside though!!

 

[atikovi]

Any opinion on using one of these devices to keep the CEL off: http://store.kteller.biz/product.asp?s=owgklf19701&strParents=&CAT_ID=0&P_ID=937&strPageHistory=search&numSearchStartRecord=1

It basically moves the O2 sensor away from the direct exhaust stream thus it doesn't sense all the HC's so it won't trigger a P0420 code. Obviously if your cat has had a melt down it won't help but if its just triggering the code now and then from old age, it may help you put off replacing the cat.

 

[columbusdude007]

I did the same and it worked!!

I have a Accord 1998 LX V6 with 175K Miles on it. The check engine light came on and I googled the problem. Read some posts on here and other websites and went to Autozone. The free code reading came up with a P0420. The next step was to check for a crack in the pipe before the CAT. Got it checked free and it was negative. Please note, if there is a crack, have it fixed first and reset the CEL and drive it around for a 100 miles before you move onto other troubleshooting steps. Then I shopped around for a CAT. Initially I bought a Universal Fit CAT for only $ 66 bucks and took it to Meineke. The guy there bitched about it not having a O2 sensor and he would have to do some cutting and welding etc and he could'nt guarantee it works!! So, I returned that and then bought a Universal Direct Fit from Autozone (make sure you also buy the gaskets) for $ 180/-. The Labor was $ 120 to fit the CAT and reset the CEL. Total cost $ 300/-. I drove the car for 100 miles and then took it for Inspection. It passed!!

The check engine line (CEL) came on and we took it to Autozone to get a free code reading. It was P0420, which turned out to be a very popular code for all Honda Accords. We have a 1999 Honda Accord LX with 140K miles. We called several local Honda dealership and received an estimate of $1K to replace the catalytic converter (CV). This has to be done in order for our 1999 Honda Accord LX to pass the State of Texas annual inspection. We took our vehicle to a highly recommended muffler shop and they replaced an after market CV, with the total cost less than $300. It has been a year now and the CEL has not come on and needless to say, our vehicle passed the annual inspection.

I have done quite a bit of research on this P0420 code and there are a lot of good recommendations. I have tried all of the home-remedies and none seems to work for me (ie. add fuel additive chemical into the gas tank, rev up the engine at a lower gear on the
highway, erase the computer code, buy super unleaded gas, replace OS2 sensor, get a tune-up, replace spark plugs wires,
replace with Honda manufactured CV, and etc....)

This has proven to be an easiest method of fixing P0420.

Good Luck !

 

[Frisbeeman43]

So I like everyone else on this forum have the infamous P0420 code. I replaced my Catalytic Converter (CAT) about 2 years ago and it has been about 25,000 miles tops since the replacement. At this point in time should I go ahead and replace the oxygen (O2) sensors? I have a 1997 Honda Accord LX 2.2L, 5 speed. I don't think the O2 sensors have been replaced at all. Has anyone had to replace anything else besides the O2 sensors and/or CAT?

 

[columbusdude007]

Check Engine Light back on..

I have a Accord 1998 LX V6 with 175K Miles on it. The check engine light came on and I googled the problem. Read some posts on here and other websites and went to Autozone. The free code reading came up with a P0420. The next step was to check for a crack in the pipe before the CAT. Got it checked free and it was negative. Please note, if there is a crack, have it fixed first and reset the CEL and drive it around for a 100 miles before you move onto other troubleshooting steps. Then I shopped around for a CAT. Initially I bought a Universal Fit CAT for only $ 66 bucks and took it to Meineke. The guy there bitched about it not having a O2 sensor and he would have to do some cutting and welding etc and he could'nt guarantee it works!! So, I returned that and then bought a Universal Direct Fit from Autozone (make sure you also buy the gaskets) for $ 180/-. The Labor was $ 120 to fit the CAT and reset the CEL. Total cost $ 300/-. I drove the car for 100 miles and then took it for Inspection. It passed!!

It has been a 1000 miles and less than a month since I passed the Inspection and the Check Engine light came on again. I took it to the Auto Zone and the guy said, I need to replace the O2 Sensor!! Has anyone faced this problem? Since I don't have to take in my vehicle for inspection for another 2 yrs, should I just let it be without trying to replace the O2 Sensor?

 

[columbusdude007]

Seems to be the remedy..

When my Accord Check Engine light came on I changed the O2 sensor on the manifold (109 K). Shortly thereafter the light returned. I then changed the O2sensor on the cat converter and in about 10 days the light went out and has stayed out "knock wood" for the last couple years (134 K). The mileage was somewhat better before I changed the sensors but the performance was better after. I was told that you can sometimes smell the converter when it is going bad. A sulphur smell. Anyone heard of that? Seems likely that changing the sensors, although a bit costly, after 100 K is a common remedy. I uses Bosch after market but still cost about $180.

It makes me feel that I replaced the wrong part!! I had actually replaced the CAT and got my Inspection passed and the light returned within a month after the Inspection! Maybe I shoulda started with the O2 Sensors first and may not have to replace the CAT!!

 

[Ralph]

This problem sucks! I have had two cheap Midas cats and now the code is set again (99 Odyssey, so far so good on the 02 Accord with 120k). I don't know what the answer is but it sure is frustrating and expensive for a LOT of people. The time, effort, and money wasted on this dubious issue is HUGE.

 

[Bruce Hawkins]

How about the rear 02 sensor?
Check life data, look for FI Temp sensor (forgot honda jargon name) should be 180-190F (Mine is 182-188F).

 

[Bruce Hawkins]

As Princess posted, the first things mentioned need to be checked, but also the car needs to be scanned with a Honda scanner to make sure the car is in proper fuel control, the trims need to be where they should be to ensure the cat can do it's job.

ok, as a short term "fix" buy a can of carb spray cleaner.
remove the intake duct leading to the throttle body.
use your hand to rev the engine and start spraying cleaner into the throttle body.
run nearly the whole can through it. make it run rough, but don't stall it.

Do this outside, the car will emit some horrendous smells and toxic fumes. The cat will begin to heat up severely as it burns up the unburnt carb cleaner and fuel. This usually works on cars that use oil, the engine oil, especially thrifted oils leave deposits on cats that poison them. If the cat's precious metal washcoat has become ineffective or the substrate has broken up, this will do no good.

When done, go out and beat the snot out of the car.

I've had some luck in keeping the P0420 away for a while this way.

I'd say on 99% of the cars once they start setting a P0420 the cat is dead or dying and needs to be replaced. The PCM in all newer cars are very, very good at what they do when it comes to catalyst monitoring. There are some cars that had too tight tolerance for that monitor and needed to be "desensitized" by having a reflash. The gen6 accord isn't one of them, neither is the Ody as far as I know.

Replacing air/fuel and the rear monitor o2 sensor won't do anything. If those sensors have an issue, normally they will set codes themselves for performance issues, i.e. slow response, etc.

Not in my case. My P0420 was the rear sensor...

Things checked:
My CAT was running a 120F difference between in/output (a short 10 minute drive was done for the worm up).
A smoked up the tail pipe test, checked for leaks. None found.
Both front and rear sensors (voltage) moved more than expected. Rear seemed to me to be slow. Rear should not move much. The rear was somewhat matching the front. Now (rear) is ~0.7V (I forgot), stays steady now...

May have been originally effected by a lazy thermostat, as my car was running at 150-180F, mostly at 168F. After replacing the thermostat its now 182-188F.

In total, I replaced the:
Thermostat, it was bad, it was sticking open sometimes.
Front sensor, the mechanic thought it mite be bad. I thought it was the rear sensor. It had no effect once replaced.
Rear sensor. No MIL for over one month...

Nither front or rear sensor, failed any test. However, the rear one was bad...

 

[nosaj81]

Hello my name is Jason and I'm new to this forum. I was surfing the net looking for the engine code for the 2010 accord coup 4cyl. While doing so I stumbled upon this thead and was intrigued. Mainly because I was having somewhat of the same problem with my 05 Scion tC that I recently got rid of. The only difference was I knew why and what the problem was. For me it was because I change the header out for performance and as soon as I did I threw the same code. when that code came up it not only said bank1 was high but bank 2 was high and vice versa. to fix the problem I had to put this in:

http://www.robearracing.com/pd-megan-racing-angled-02-simulator-cel-fix.cfm

I only put 1 in on bank 2 and that cleared up the problem with bank 2.

Now my question to you guys is did this problem start happening with your stock header/s or did you guys change them out for aftermarket.

 

[Bruce Hawkins]

I was stock. If your loosing heat, it's possible to have CAT efficiency problems. Rapping the header, probably would help...

So U replaced the rear sensor too???

 

[crust]

99 accord ex v6

Recognizing this thread is old, I had the P0420 for a brief period (1 week maybe), then the P0401 (I think) code for a while. I asked the dealer to check it out and they found nothing wrong with the cat. So I went ahead and did the EGR service myself, took off the intake, cleaned out the pipe, etc. Car passed the state inspection, but then 2 days later and probably not more than 100 miles. The P0420 code returned. At this point not sure what to do.

I did put a fancy scanner on the car and plotted the output of the O2 sensors. It seems the downstream sensor is tracking the upstream sensor closely. This leads me to think the cat is doing nothing. I just spent $2500 to have the tranny and axles replaced at the dealer so I still have a 3 yr warranty on that.

Any thoughts? If I go to replace the cat, the dealer is spendy ($1000) but I can buy the honda cat online for $700 or so. Is it easy enough to myself?

Thanks

 

[wcbillyball]

P0420 engine code

I have a 2001 Accord LX 2.3 4 cyl 200k miles with check engine light on. It will not pass smog. Engine code P0420. I was told it could be the Cat, or one of the two oxygen sensors. I replace the two Oxygen sensors because that was cheaper than a new Cat. No Change. The dealer wanted $1,400 for the cat. I found a local muffler shop who install a new after market cat with warrenty for $230. That solved the problem. Dealer told me code P0420 is always the cat.

 

[Bruce Hawkins]

I have a 2001 Accord LX 2.3 4 cyl 200k miles with check engine light on. It will not pass smog. Engine code P0420. I was told it could be the Cat, or one of the two oxygen sensors. I replace the two Oxygen sensors because that was cheaper than a new Cat. No Change. The dealer wanted $1,400 for the cat. I found a local muffler shop who install a new after market cat with warrenty for $230. That solved the problem. Dealer told me code P0420 is always the cat.

That's what they think. BTW, the replacement CAT you got is likely not the correct type CAT, unless you have LEV engine. Did you pull fuse 13 or erase the stored code? The CAT is that expensive because its different that 99% CAT's out there. How a SMOG tech would know, weather a car has the right CAT, I dont know...
Good luck!

 

[myreikko]

Hey guys,
I'm glad I found this thread, know it's old too, but sadly my 6th gen experienced the CEL today. I've notice it before. Usually it blinks 3-4 times after I start the car, but it would just go back to normal. Though today is totally different and got me depressed. Turned on my car and it acted funny. The CEL won't turn off this time. It felt like it was having a hard time and sounded like the engine was gonna die. I turned on the AC and it started chugging, so I turned it off right away. When I pressed on the break and gas pedals, they felt very stiff. When I finally drove it, it felt like the car was having a hard time with power. Usually pushing the gas pedal a lil, the car would just excel lively but today she felt weak =[. The trembles were harder this time, and I was soo scared it was gone die in the middle of the road. After I got to the bank and started her again to get back to work, she seemed a lil bit ok, but the CEL was still on. She still felt weak with excelling and I didn't wanna drive her over 35MPH. So does this mean I have the dreaded P0420 code as well =,[?? I can't seem to understand it though cause she's only at 80+k.......

 

[drozzin]

Get your code read and then we can discuss something.

 

[Bootzilla]

Hey guys,
I'm glad I found this thread, know it's old too, but sadly my 6th gen experienced the CEL today. She still felt weak with excelling and I didn't wanna drive her over 35MPH. So does this mean I have the dreaded P0420 code as well...

Definitely scan it - you can pick up an OBDII reader pretty cheap. What does it do at idle? If it stumbles and shudders, and then continues to shudder just off idle when you press the gas pedal, it could be the upstream O2 sensor. If, though, it feels like nothing is happening when you try to accelerate, the cat could be breaking down inside and plugging up - if that is the case, eventually it will worsen to the point where you won't even be able to keep up at highway speeds (ask me how I know! Our accord went from fine to no faster than 45 mph over one weekend).

But the codes are what you want next. If you don't want to get a reader, the popular auto stores should hook you up for free.

Continuing the topic - we've got an '00 accord ex with the LEV 4-cyl. Replaced the front O2 sensor about 4 years ago (we got the p0420 and whatever the front sensor code was that time, along with driveability problems), then about a year and a half ago the cat self-destructed and was replaced (P0420 as well as the symptoms I referred to above).

Now I just got a CEL tonight - P0420 again, but no obvious driveability problems. I think I'm going to start with the rear 02 sensor since it is original with 127k on it, have a look at the EGR condition and then go from there - hopefully it won't be another cat, but I'll post what I find in case anyone else can get some use from it. Daggone thing runs great, otherwise!

Todd.
.