catalitic converter problem - Toyota Yaris Forums

mariann · 01-12-2013, 03:27 AM

i have replaced my catalytic converter after getting p0420 cat blelow treshold problem.
it ws fine for 3 months and 5000Km. now i'm getting this problem again!
how can i check if something keep destroilng my cat?
i cant hear any backfire or something wrong there.
what can i do now?
last time i had it i needed to repalce also lambda sensor....

CTScott · 01-12-2013, 06:54 AM

Ideally you need to measure your AFR (air to fuel ratio) to see if the engine is running particularly rich, which would plug the CAT over time. Some of the OBDII scanners can display AFR. They tend to have a lag, versus a real AFR gauge with its own sensor, but for just watching the AFRs, an OBD scanner would be fine. Over here, where many states have emissions testing for vehicles, repair shops have a tool that they stick up the tailpipe to measure the car's output. That is also a good way of seeing how the engine is running.

mariann · 01-12-2013, 03:26 PM

i can see the volts graph of the fuel air ratio. its running up and down from 0.1V to 0.8V...
we have this emmision yearly test with the prob inside the exhaust pipe wich masure 4 gasses.
the last time i did it i past the test fine with bad cat...
can it be a poor quality (but made in US with Chip Foos picture on the box) cat? or still something in my engine messing it up?
shuld i change sparkplugs or adding this fuel cleaner can to the tank?

CoryM · 01-12-2013, 09:02 PM

The two most common causes of failed catalytic converters are:
-engine burning oil. This causes too much fuel for the catalyst to react with, and it melts.
-vibration. Such as a broken exhaust support bracket, or even just a rattling heatshield.

It is also very common for inexpensive aftermarket cats to only last a year or two; Even in good conditions. They use the bare minimum of the expensive catalyst materials to meet OBDII requirements (and sometimes not even that).

Yes, over-fuelling can cause cats to fail (same reason as the oil), but newer cars are much less likely to over-fuel that much without throwing a code.

Do you notice any blue smoke from the tailpipe when starting it cold? Any buzzing or rattling noises from the exhaust?

01-12-2013, 03:27 AM	#1
mariann Drives: yaris 2007 Join Date: Mar 2009 Location: israel Posts: 39	catalitic converter problem i have replaced my catalytic converter after getting p0420 cat blelow treshold problem. it ws fine for 3 months and 5000Km. now i'm getting this problem again! how can i check if something keep destroilng my cat? i cant hear any backfire or something wrong there. what can i do now? last time i had it i needed to repalce also lambda sensor....

01-12-2013, 06:54 AM	#2
CTScott ULTIMATE View User's Garage Drives: 09 5dr LB, 2x 08 3dr LB Join Date: Oct 2008 Location: USA, CT Posts: 13,460	Ideally you need to measure your AFR (air to fuel ratio) to see if the engine is running particularly rich, which would plug the CAT over time. Some of the OBDII scanners can display AFR. They tend to have a lag, versus a real AFR gauge with its own sensor, but for just watching the AFRs, an OBD scanner would be fine. Over here, where many states have emissions testing for vehicles, repair shops have a tool that they stick up the tailpipe to measure the car's output. That is also a good way of seeing how the engine is running. __________________

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01-12-2013, 03:26 PM	#3
mariann Drives: yaris 2007 Join Date: Mar 2009 Location: israel Posts: 39	i can see the volts graph of the fuel air ratio. its running up and down from 0.1V to 0.8V... we have this emmision yearly test with the prob inside the exhaust pipe wich masure 4 gasses. the last time i did it i past the test fine with bad cat... can it be a poor quality (but made in US with Chip Foos picture on the box) cat? or still something in my engine messing it up? shuld i change sparkplugs or adding this fuel cleaner can to the tank?

01-12-2013, 09:02 PM	#4
CoryM Drives: 2009 5-door, 5-speed Join Date: Sep 2011 Location: White Rock BC Posts: 687	The two most common causes of failed catalytic converters are: -engine burning oil. This causes too much fuel for the catalyst to react with, and it melts. -vibration. Such as a broken exhaust support bracket, or even just a rattling heatshield. It is also very common for inexpensive aftermarket cats to only last a year or two; Even in good conditions. They use the bare minimum of the expensive catalyst materials to meet OBDII requirements (and sometimes not even that). Yes, over-fuelling can cause cats to fail (same reason as the oil), but newer cars are much less likely to over-fuel that much without throwing a code. Do you notice any blue smoke from the tailpipe when starting it cold? Any buzzing or rattling noises from the exhaust?