P0420 Catalyst System Efficiency Below Threshold

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I am getting this code on my ECHO with a check engine light. I've been trying to read up on how to use the diagnostic information I get from my OBDII scanner and I just really don't understand what I'm seeing. Below is a typical display for the fuel trims and voltages, I'm sure that isn't good but does it indicate a bad catalyst or something else? Do I need to take more readings? Any help or suggestions would be appreciated, thank you.
 
Have you ever replaced the O2 sensors or cats in that 17 year old, 262k mile vehicle?

I'm all for actually diagnosing a problem first before throwing parts at something, but new O2 sensors certainly would not hurt!
 
Looks like a textbook bad cat

Look how the sweep of B1S1 (upstream of converter) is matched by B1S2 (after converter)

This is showing that the convertor isn't doing it's job

Either replace the post cat sensor, and put a spacer on it, or prepare to buy a new converter

Have you been driving around with a misfire?

OTOH, at 262k, it just may be worn out and done with
 
Yeah, I replaced the sensors when the code first appeared a few months back, and the check engine light went away for a while but now is back and it never leaves. There for a while it would disappear for a day or two but come back, now it stays on all the time.
 
Originally Posted By: michaelluscher
Have you been driving around with a misfire?

Not that I'm aware of, it seems to run fine. I would get some other code perhaps if that is the problem?
 
Originally Posted By: kschachn
Yeah, I replaced the sensors when the code first appeared a few months back, and the check engine light went away for a while but now is back and it never leaves. There for a while it would disappear for a day or two but come back, now it stays on all the time.


Did you use Denso Oxygen Sensors or some other after-market brand?
 
Originally Posted By: StevieC
Did you use Denso Oxygen Sensors or some other after-market brand?

They are Denso sensors.
 
I would most likely yes. On my car there's a clearly different code for misfires. I agree with the one fella who says it definitely the cat. If your voltage was all over the place with the downstream 02 sensor then it would just be that. But the voltage on both upstream and downstream sensors is corellated very well. It is the catalytic converter that's bad..
 
Originally Posted By: michaelluscher
Looks like a textbook bad cat

Look how the sweep of B1S1 (upstream of converter) is matched by B1S2 (after converter)

This is showing that the convertor isn't doing it's job

Either replace the post cat sensor, and put a spacer on it, or prepare to buy a new converter

Have you been driving around with a misfire?

OTOH, at 262k, it just may be worn out and done with


+1 to all this

If they don't do tailpipe emissions testing on your car where you live I'd put a spacer in there and cross your fingers. Aftermarket cats are garbs and factory ones are expensive.
 
Thanks for everyone's help. No, they stopped tailpipe inspections here a while back and only do the diagnostic connector test. I'll do something, I have to pass that inspection soon.
 
Originally Posted By: Seventh
Originally Posted By: michaelluscher
Looks like a textbook bad cat

Look how the sweep of B1S1 (upstream of converter) is matched by B1S2 (after converter)

This is showing that the convertor isn't doing it's job

Either replace the post cat sensor, and put a spacer on it, or prepare to buy a new converter

Have you been driving around with a misfire?

OTOH, at 262k, it just may be worn out and done with


+1 to all this

If they don't do tailpipe emissions testing on your car where you live I'd put a spacer in there and cross your fingers. Aftermarket cats are garbs and factory ones are expensive.


Looks like rockauto sells an Eastern Catalytic for about $257. Has a 5 year/50k warranty. Not as good as factory which is typically an 8/80k, but with that kind of mileage, I'm not sure how much more he was expecting. It might even be time to call it quits as that car is probably only worth 1-2k.
 
Throw a spacer (spark plug anti-fouler) on that after cat oxygen sensor and problem fixed. Buy the deep ones and you usually don't have to drill them out. Double them up too.
 
I have had two different cars that threw the catalyst efficiency codes at about 200,000 miles. On both cars I cleared the code with my scan tool and then ran a bottle of Techron fuel system cleaner through the tank. Neither car had the code come back. This was about 4 years ago and about 25,000 miles on each car.

This won't work if your converter is burned out, but if it is just dirty with soot and other combustion debris it might work for you.
 
Yeah FWIW I hooked up the scan tool to my Sienna and the voltage charts are vastly different. The voltage for sensor 2 remains virtually constant while sensor 1 does its thing. Thanks again for the help.
 
If the cat is working properly, the downstream O2 sensor (sensor 2) should be a relatively flat line while sensor 1 will have peaks and valleys. Your two sensors appear to be mirroring each other; if this continues to happen after spending a bit of time on the freeway, the cat isn't doing its thing.
 
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