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Need help - check engine light code p0420

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Old 12-31-2011, 01:26 PM   #1
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Need help - check engine light code p0420

My check engine light came on, had Autozone test it and it came back P0420 – Catalyst System Efficiency Below Threshold.


Tacoma 2003 2wd 4cyl 178,000 miles runs fine, never have had a major problem.


I called a dealership and was told if I needed a new converter it would cost $1500-2100 depending on the type I needed.


A call to a muffler franchise said $449 or much less if it was a sensor problem. Obviously I won’t be going to the dealer.

(1) I had a new muffler put on about 13,000 miles ago, could that have caused the problem?
(2) What questions should I ask when I bring it to the repair shop?
(3) I was thinking of bringing it to a muffler franchise to have it done. Is one of the national chains better than the others?
(4) I have very little mechanical experience. Is there anything I could visually check though before I bring it in?

Thanks for any help/advice!

Tom
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Old 12-31-2011, 01:42 PM   #2
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If the ecm is giving you that code its not the sensors you can 95% rule that out.

your cat is bad of course.

You can buy a cat from online and have a shop put it on for you. All that holds the cat in place is 4 bolts.

One thing i would do is check to make sure from toyota the cat is still not in warranty.(never hurts to ask)
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Old 12-31-2011, 08:14 PM   #3
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After I started this thread today I drove the truck for about 20 miles, stopped for an hour and when I started the truck again the check engine light didn't come on. It stayed off the 20 mile trip back home.
Any thoughts?
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Old 12-31-2011, 08:18 PM   #4
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last time i had that code it wound up being my 02 sensor, i replaced both the 02 sensor behind the cat and the fuel air ratio sensor in the front, use only OEM sensors though, our trucks are funny about that.

a CEL that comes on and off means it can be potentially harmful to the catalyst system
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Old 12-31-2011, 08:30 PM   #5
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Quote:
Originally Posted by hayabusa3303 View Post
If the ecm is giving you that code its not the sensors you can 95% rule that out.

your cat is bad of course.

You can buy a cat from online and have a shop put it on for you. All that holds the cat in place is 4 bolts.

One thing i would do is check to make sure from toyota the cat is still not in warranty.(never hurts to ask)
Though his truck is 8 years old and emissions warranty would be up to 8 years, he has 178,000 miles, WAY out of warranty.
Quote:
Originally Posted by fireturk41 View Post
last time i had that code it wound up being my 02 sensor, i replaced both the 02 sensor behind the cat and the fuel air ratio sensor in the front, use only OEM sensors though, our trucks are funny about that.

a CEL that comes on and off means it can be potentially harmful to the catalyst system
Not sure if you ment what i'm about to state, but a cel that is flashing constantly indicates the problem may be harmful to the well being of the cat. Not if it comes on and then goes off.
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Old 12-31-2011, 08:32 PM   #6
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Quote:
Originally Posted by Toyota Tech31 View Post
Not sure if you ment what i'm about to state, but a cel that is flashing constantly indicates the problem may be harmful to the well being of the cat. Not if it comes on and then goes off.
yeah thats it im just not good with words haha
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Old 01-01-2012, 06:41 AM   #7
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My truck threw this code a while ago. It ended up being an exhaust leak. It's worth checking for that before doing anything else, at least in terms of $.
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Old 01-01-2012, 06:51 AM   #8
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My truck also threw this code a while back after I changed the place where I got gas, went back to the old place and it's been gone ever since.
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Old 01-01-2012, 07:40 AM   #9
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Quote:
Originally Posted by tomd View Post
My check engine light came on, had Autozone test it and it came back P0420 – Catalyst System Efficiency Below Threshold.

Tacoma 2003 2wd 4cyl 178,000 miles runs fine, never have had a major problem.

I called a dealership and was told if I needed a new converter it would cost $1500-2100 depending on the type I needed.

A call to a muffler franchise said $449 or much less if it was a sensor problem. Obviously I won’t be going to the dealer.


(1) I had a new muffler put on about 13,000 miles ago, could that have caused the problem?
(2) What questions should I ask when I bring it to the repair shop?
(3) I was thinking of bringing it to a muffler franchise to have it done. Is one of the national chains better than the others?
(4) I have very little mechanical experience. Is there anything I could visually check though before I bring it in?

Thanks for any help/advice!



Aftermarket cats can be crap, I went that route on my 84 240 Volvo and 2 years later I had to replace it again, same thing happened again on the next smog check. After that I bought my third new cat, I only put it on for the test and then took it off and put the old one back on, I did this for several years before getting rid of the car.

Tom
Quote:
Originally Posted by tomd View Post
After I started this thread today I drove the truck for about 20 miles, stopped for an hour and when I started the truck again the check engine light didn't come on. It stayed off the 20 mile trip back home.
Any thoughts?
Hmmm, bad gas?

Quote:
Originally Posted by steveOtacO View Post
My truck threw this code a while ago. It ended up being an exhaust leak. It's worth checking for that before doing anything else, at least in terms of $.

Worth looking at.


Quote:
Originally Posted by magog45 View Post
My truck also threw this code a while back after I changed the place where I got gas, went back to the old place and it's been gone ever since.

Again, worth a try. This happened on my sons Camry on his trip to California from Texas coming through El PAso, gassed up in El PAso and got the code several times on that tank and did not get the code again until his trip back, again after gassing up is El Paso, from the same gas station.
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Old 01-01-2012, 07:42 AM   #10
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Quote:
Originally Posted by tomd View Post
My check engine light came on, had Autozone test it and it came back P0420 – Catalyst System Efficiency Below Threshold.

Tacoma 2003 2wd 4cyl 178,000 miles runs fine, never have had a major problem.

I called a dealership and was told if I needed a new converter it would cost $1500-2100 depending on the type I needed.

A call to a muffler franchise said $449 or much less if it was a sensor problem. Obviously I won’t be going to the dealer.


(1) I had a new muffler put on about 13,000 miles ago, could that have caused the problem?
(2) What questions should I ask when I bring it to the repair shop?
(3) I was thinking of bringing it to a muffler franchise to have it done. Is one of the national chains better than the others?
(4) I have very little mechanical experience. Is there anything I could visually check though before I bring it in?

Thanks for any help/advice!

Tom


Aftermarket cats can be crap, I went that route on my 84 240 Volvo and 2 years later I had to replace it again, same thing happened again on the next smog check. After that I bought my third new cat, I only put it on for the test and then took it off and put the old one back on, I did this for several years before getting rid of the car.

Quote:
Originally Posted by tomd View Post
After I started this thread today I drove the truck for about 20 miles, stopped for an hour and when I started the truck again the check engine light didn't come on. It stayed off the 20 mile trip back home.
Any thoughts?
Hmmm, bad gas?

Quote:
Originally Posted by steveOtacO View Post
My truck threw this code a while ago. It ended up being an exhaust leak. It's worth checking for that before doing anything else, at least in terms of $.

Worth looking at.


Quote:
Originally Posted by magog45 View Post
My truck also threw this code a while back after I changed the place where I got gas, went back to the old place and it's been gone ever since.

Again, worth a try. This happened on my sons Camry on his trip to California from Texas coming through El PAso, gassed up in El PAso and got the code several times on that tank and did not get the code again until his trip back, again after gassing up is El Paso, from the same gas station.
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Old 01-01-2012, 07:44 AM   #11
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Just throwing my cents in. CEL came on in my truck, same code. Ran a can of Seafoam through the intake and fuel tank and now all is good.
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Old 01-01-2012, 10:06 PM   #12
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mine would stay off for some times up to 120 miles. Then it got more frequent.

I replaced both O2's and my cats with some aftermarket ones, total cost was under $400, and it's super easy to swap the old cats out. As long as your bolts aren't rusted to shit like mine were.

My .02$ - start with the sensors.
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Old 01-02-2012, 10:53 AM   #13
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same code put on a magnalfow cat and 2 new o2 sensors code gone. total cost 250 i put it all on my self saved alot that way. amazon.com
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Old 01-13-2012, 05:30 PM   #15
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My Tacoma has now gone about 600 miles without the light coming back on so I'm hoping no news is good news. Thanks to all for your help!
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Old 01-13-2012, 09:39 PM   #16
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Since your in Boston, this might be of interest to you as you have to get emissions testing done (I live in Mass also):

1) Try Cataclean (seach the name in google and you can see what it is) if the light comes back on before dumping tons of money into the cat. It worked for me and was recommended by a Toyota mechanic. It got the check engine light to go out and for me to pass emissions testing. Now, I can drive on the thing for another year with the light coming on if it is just the cat throwing the code.
The rest of this is just helpful information:
2) P0420 is a shitty code in that it can mean more then one thing. It can be faulty 02 sensors as there is one upstream 02 sensor before the cats (there are two cats on the V6 models at least) and then one downstream 02 after the cats. The ECU reads the difference in exhaust between the two 02 sensors after the exhaust has passed through the cats to determine if the cats are doing their job correctly. If the 02 sensors are faulty then it can give you a P0420.
3) However, 95% of the time, it is the cat(s) itself which are really expensive if you go OEM. Second, there are actual codes (I am pretty sure) for the 02 sensors so again, it is almost always the cat(s) but not always. This comes directly from a Toyota mechanic (not me, just someone I know).
4) If the check engine light comes on and goes off and then stays off then no problem. If it blinks constantly while driving, big fu.... problem. That means stop driving. However, it is normal for it to come on and then later go off and stay off when it is P0420. That simply means the code is no longer being sent to the ECU. Mine did that also.
Good luck since the light is now out!
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Old 02-09-2012, 06:47 PM   #17
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Question P0420

had this code come on a week ago and was woundering if a leak at the rear 02 sencer would cause this code ? excuse my spelling lol
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Old 06-01-2013, 06:15 PM   #18
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Been reading this old thread with interest.

My '95 threw a P0125 code recently. I replaced the air/fuel sensor in front of the cat with a Denso. Reset the code and the light stayed off. For about an hour.

Now I have a P0420.

I read somewhere that some guys think it's a good idea to replace the rear O2 sensor at the same time the front one is replaced. In other words to always replace them together.

Anyone have any thoughts? I reset the P0420 and I'll know tomorrow if it comes back or not.
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Old 02-07-2014, 07:56 PM   #19
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so I got the P0420. I replaced both with flowmaster high flow cats and reset the ECU and no problems here. sounds better too
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