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How to Fix a p0420 Catalyst System Efficiency Below Threshold Bank 1

December 2, 2019

Hello welcome to my video on this car we have the engine light on as you can
see this is one of my customers cars okay iv plugged in my laptop with the diagnostics plugin we have a P0420 catalytic system efficiency below threshold which is not a good sign
for the catalytic converter so what I’m gonna do now is clear the
codes ok press yes here and now as you can see codes have
actually gone and we gonna go to live Data now on the left we got bank 1 sensor 1 oxygen sensor on the rite we got bank 1 sensor 2 oxygen sensor output voltage for both so iv started the car now I heated the car up iv pre heated the engine up 2000 rpm now so far so good its in closeloop which means the catalytic converters heated up you can see that sensor 2 is mimicking sensor 1 now which is telling me that the catalytic
converter is not Converting the gases you would expect
it to stay in one line at a roundabout 4.5 to 8 mv the sensor 2 should be 4.5 to 8 mv in one straight line which is not sensor 1 as you can see as you can see sensor one should be going up and down as it is so if you look at sensor 1 its going up down up down which is fine sensor 2 its going up down up down which is not fine so it’s mimicking sensor 1 so if you get this kind of Code see
something like this then near enough it guarantees that the catalytic converter is not doing
its job so it’s not converting the gases with this particular car this
is my customers car I mean some people take the cat and they dip it into soap or put cat cleaner in the fuel I would advise that if its not too expensive then your better of just changeing the catalytic converter and on my customers car its gonna cost
about 150 pounds I think it was 160 pound im just gonna change the catalytic converter I’m gonna make another video me changing the catalytic converter which will be part 2 and part 3 will be I am going to plug it all back in and where going to have another look at the readings so i hope you’ve enjoyed my video and
learned something from it and I hope to see you in my next video part 2 and part 3 see you soon thank you bye

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  • Reply Recovering New Yorker October 4, 2014 at 12:49 pm

    Hello! Shep in Florida here. "Riddle me this Batman". Can a catalytic converter just go bad? I'm a retired tech and have been taught that cats don't just die. They're murdered. 3 years ago I installed a new (not reman) engine in my 2000 Chevy S10 (small US made pickup truck) along w/other related parts.Chief among them a new aftermarket cat from Walker emissions. The former owner failed to maintain the truck and at 100,000 km the cat clogged and engine over heated and cracked. 8 months later a p0420 code appeared. The truck runs great and I couldn't find any vac leaks,misfires, additional codes,etc.The auto parts store replaced it for me at no charge and I installed it. 1 week ago the p0420 code came back. Same conditions. Again, I installed it. When the mil appeared I ran a live data test. The post o2 sensor was reading all over the map (between .11  and .91 volts) All other readings normal. After the 2nd cat was installed the readings were between .73 and .78 volts at highway speeds and between .44 and.48 at idle. Any Ideas? Some of my tech associates say I need a factory cat ($2000). While others say an after market cat ($179-$371) should be just fine. Thanks and I await your answer. 

  • Reply E Buzek May 26, 2015 at 11:28 am

    Wouldn't it also be a good idea to check the inlet and outlet temps of the catalytic converter because their could be issues with the downstream sensor?  Get it to operating temp, 1 person keeping it at about 2000 – 2500 rpm and another underneath taking temp readings. Down stream should be higher.

  • Reply Jester 21 February 24, 2017 at 7:15 pm


  • Reply John Carpa April 3, 2017 at 7:30 am

    Why some jerks would give him thumb down!

  • Reply Grant Honderich May 24, 2017 at 1:24 am

    I can make it all go away by a bunch of resistors faking the voltage wanted! and ready inside ten mins for $5 but if you want a plug and play $150. Just did mine and I DONT EVEN HAVE CATS!! lo;l

  • Reply MINABDO for auto rapair April 2, 2018 at 8:21 am

    very good thank you so mucth

  • Reply Spiro Ndimaris June 8, 2018 at 8:15 pm

    good job keep up the videos

  • Reply Mind Over Matter January 22, 2019 at 5:19 am

    I have a question ,my 05 toyota 4runner has a p0420 the truck is running
    perfect but is burning more fuel than normal i can tell,b1s2 is
    mirroring b1s1 is that mean i need a cat? there's all kinds of
    information out there,it doesn't really feel like the cat i clogged what
    should i do? Thanks

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