P0420 code
 

anyone here had any experience with using the 02 sensor spacers available on ebay,to render the problem of setting the P0420 codes???( cat efficency below threshold,etc).... i have replaced the front 02 senors,replaced the cat.twice!and still get the P0420 code from time to time,and it is getting more frequent now....I read somewhere that the spacers will remedy this as they reduce the amount of info the sensors read,but yet no harm to the engine or componets.......

When the PCM runs the converter monitor, it is looking for very specific changes in data from all of the oxygen sensors, in a specific time frame. If the data is incorrect, or at the wrong time, P0420 sets in memory. P0420 is one of the easiest DTC's to diagnose, if you follow the flow chart. https://blazerforum.com/forum/diagno...plained-19820/

Any electronic device, or spacer that is installed to "fool" the PCM, ain't gonna work. There are two ways to eliminate the P0420: #1 fix the problem. #2 find someone that will reprogram the PCM to disable the converter monitor. Good luck with that one ;)

Thank you very much or the informative and detailed info....so many things can trigger the P0420!!! and I agree that finding the real problem is the way to go here....but that is pretty much the problem....so far noone has nailed down the exact reason for the code?????
And with all due respect....I just talked to a guy yesteday who runs a well known performance /speed shop here about the spacers and he says he has used them with great success especially when installing headers,custom exhaust systems,etc...they are actually marketed as for Off road use Only....and according to him they just limit the amount of info the 02 senors read and prevent the setting of the code P0420,and I do understand it is not fixing the problem causing the illumination Ckeck Engine. and at the same time the spacers cause no engine damage or to other components.....so it seems to be a "catch 22" situation .....50% one way,50% the other way....and for just $20 for two spacers,It might be worth a chance to try them (in my case) as opposed to hundreds of dollars to try and nail down the real cause (and there are many it appears) A few have even said it may be high dollar PCM problems! if the spacers don't work,not much lost....

ive seen this pop up a lot lately. im kinda curious as to if they work but yeah evertime ive ever seen the 420 code its always a cat. everyone i know who tries to change the 02 sensors just gets the code right back.

you can be the lab rat for us, try them out and let us know if it works. im kinda curious myself. everything i own is pre 95 so thats my way of dealing the p0420 :)

B1S3, (downstream oxygen sensor) should report a low steady voltage when the converter is doing its job. During normal driving, with the sensor spaced back out of the exhaust flow, B1S3 output voltage will be lower than normal. The PCM should interpret this as a good converter. When the converter monitor runs, B1S3 will report the mixture changes at a lower voltage, which may or may not set the P0420. However, it's more likely to set a P0143 and or P0146. End result, you still have the check engine light on, a false P0143/P0146, and a P0420 that the PCM is not recognizing. Better to fix it properly, than to create and chase other problems.... just my opinion ;)

Guess I will be the "lab rat" here as Nonone I have been to can nail down the real cause for my 420 code! this is the 3rd cat on it now since 2003,02's changed with good quality ones $$!!!still to no avail....One article I read said can be as simple as bad fuel (with a high sulphur content or lead?????) and I have no exhaust leaks,therefore again some say bad PCM! runs mighty good and smooth for a bad PCM is all I know ??? So I don't know or anyone else? what's setting the P0420 on my 2003 with only 95,000 miles 4.3 engine?????
Yes, classic cars(pre1970's!) looking better to me more and more! they don't have these crappy issues with PCM's,codes, expensive parts as in Cats!!.etc. etc....only going to get worse guys with all this so called hi-tech cars...I am from the old school and still love and perfer the simple V8's with a good carburetor,no emessions,and a simple point/condenser distributor....and with a hell of a lot more HP and "get up and go"

A few years ago, GM had a TSB that addressed the issue. The PCM was programmed so P0420 would not set so easily, (widened the set parameters). The TSB was for L/M models and may have included S/T models too, can't remember for sure.

a lot of the new aftermarket cats out there are just garbage. seems anytime we every put a walker or magnaflow cat on a car, they come right back 1-2 years later for another cat code. so every year or so you have to re-replace the cat.

in illinois anything older then a 95 doesnt have emissions. i daily drive a 1990, soon as this thing falls apart im going down south to get a rust free one, i really dont want to mess with this emissions stuff.

Exactly my reason for looking around and trying to buy a nice classic(pre1970's) and yes a nice classic will cost you dearly these days....still a better choice as far as I am concerned!at least you can work on them a little yourself and get to most every component on it with just some basic hand tools....

This is what I have thought all along....it is a racket!! for selling expensive parts for GM....a cat. that is working at say 95% or a little under is just as good as 100%!! ,but yet their standards and parameters are programmed so as to set these codes knowing the consumer will run out and buy a high dollar cat. just to comply to the standards or fix the problem(not really a problem though!)but the average consumer doesn't know this?Lets get real here! a 95% working cat. is as good as 100% in realality and anything below 95% needs replacing????????????