02 sensor/P0420 problem

[deviantmr-s]

From memory, the post-cat sensor is located on the cat assembly itself. Is there any chance that the aftermarket location is on a poor point?
Though this might also mask any underlying problems and make the car run improperly, have you tried a non-fouler?

It is in the same location as the standard. I would rather not try a non-fouler, for the reason you mentioned.

[thetyrant]

Can anyone with a known good cat and post lambda sensor do a graph log on torque at both idle and fast idle (2500rpm area)  ?   just want to know the sort of numbers a healthy setup gives from the post cat sesnors

[deviantmr-s]

Can anyone with a known good cat and post lambda sensor do a graph log on torque at both idle and fast idle (2500rpm area)  ?  just want to know the sort of numbers a healthy setup gives from the post cat sesnors

This would be extremely helpful to check against.

Anyone?

[shnazzle]

Can anyone with a known good cat and post lambda sensor do a graph log on torque at both idle and fast idle (2500rpm area)  ?  just want to know the sort of numbers a healthy setup gives from the post cat sesnors

This would be extremely helpful to check against.

Anyone?

Unfortunately I can't help as I have a sports cat, so my values are a bit off anyway.

[thetyrant]

Unfortunately I can't help as I have a sports cat, so my values are a bit off anyway.

Would still be interesting to see the numbers, if the sport cat is a good one and has passed mot emissions the numbers shouldnt be that far different for what im looking for.

[deviantmr-s]

Unfortunately I can't help as I have a sports cat, so my values are a bit off anyway.

Would still be interesting to see the numbers, if the sport cat is a good one and has passed mot emissions the numbers shouldnt be that far different for what im looking for.

Two new sensors and just been for emissions check and it would fail.

[Carolyn]

Points to the cat, I'm afraid.

[thetyrant]

Two new sensors and just been for emissions check and it would fail.

Bugger looks like maybe your cat then,  presuming you got the cat nice and hot before he tested it ? 

Did you see numbers from emissions test to show how far out you are ? a failed cat should be miles out from the required CO requirements

[deviantmr-s]

Two new sensors and just been for emissions check and it would fail.

Bugger looks like maybe your cat then,  presuming you got the cat nice and hot before he tested it ? 

Did you see numbers from emissions test to show how far out you are ? a failed cat should be miles out from the required CO requirements

Yes nice and hot and miles out.

I have emailed Proflow for their advice and guidance, and await a response as to what cat I should replace in their system - but any advice would be greatly appreciated from you guys of infinite wisdom.

But be gentle with me, learning as I go...
 

[shnazzle]

Get a bottle of cataclean on half a tank and givr the a good seeing too. Work that cat. See what it does. That's my only thought. 
If your short term fuel trims and long terms are fine,your cat is dead unfortunately

[deviantmr-s]

Get a bottle of cataclean on half a tank and givr the a good seeing too. Work that cat. See what it does. That's my only thought.
If your short term fuel trims and long terms are fine,your cat is dead unfortunately

Already had two lots of cataclean through... seems dead in the water.

[thetyrant]

Ok little update from me on this, went over the cars intake last night removing the airbox and all pipework to check and refit, nothing obvious found but now know its all on properly (unlike some other things previous owner did!) also fitted new NGK plugs and had battery off while doing all this to reset all fuel trims etc.

Once back together went for fresh tank of fuel and then a blast up the local test route to Hartside summit , car does seem to run a little smoother and pulls nicely enough, readings from the post cat sensor by time i was heading home with a nice hot exhaust seemed to of improved as well but im still not convinced cat is working as it should, i scanned for codes when i got home and P0420 was present (wasnt before i set off) but could be down to cat not getting upto temperature initially maybe ?  ive reset it anyhows.

Will use car for next few days and see what happens and if code comes back, need to pop into mot place as well when i get a minute get him to put sniffer on it.

I hope thats it sorted as otherwise im going to have to refit my oe cat (after fixing flexi) and see if that sorts it.

 

[shnazzle]

Definitely get the sniffer test done after a good hard blast.The P0420 isn't an emissions code remember. It has no clue what your emissions are. It just isn't happy with the voltage the post-cat sensor is putting out over the required drive cycle.

So you may very well pass emissions with that code.

[thetyrant]

Definitely get the sniffer test done after a good hard blast.The P0420 isn't an emissions code remember. It has no clue what your emissions are. It just isn't happy with the voltage the post-cat sensor is putting out over the required drive cycle.

So you may very well pass emissions with that code.

Indeed thats my goal as car is otherwise running ok from all checks ive done, i just need to be sure it doesnt cause issues with upcoming mot especially after having just spent £140+ on new cat (all be it primarily to sort the leaking flexi) i was hoping not to have any concerns with emissions tests or other exhaust issues, then i get this code a few weeks after fitting arrgh!

Code P0420 is an emissions test of sorts providing the sensors are working of course, its telling me cat isnt converting the gas as it should just same as MOT test, of course they test for HC, Lambda and other things as well but if sensor is good and P0420 is active then mot fail is inevitable on emissions in most cases i would think.

My concern is the new cat is perhaps not up to the job and needing serious heat to switch it active, OE cats are far higher quality and no doubt start working much quicker due to this, also the extra heat shielding on OE cat will help keep it upto temperature as well as protecting things mounted around it, there is no shielding on the cats2u/BM cat and also i currently dont have nappy/undertray fitted on so maybe all this isnt helping with cat dropping out of its zone, if that is the case of course!

Pesky cars

[Carolyn]

Definitely get the sniffer test done after a good hard blast.The P0420 isn't an emissions code remember. It has no clue what your emissions are. It just isn't happy with the voltage the post-cat sensor is putting out over the required drive cycle.

So you may very well pass emissions with that code.

Indeed thats my goal as car is otherwise running ok from all checks ive done, i just need to be sure it doesnt cause issues with upcoming mot especially after having just spent £140+ on new cat (all be it primarily to sort the leaking flexi) i was hoping not to have any concerns with emissions tests or other exhaust issues, then i get this code a few weeks after fitting arrgh!

Code P0420 is an emissions test of sorts providing the sensors are working of course, its telling me cat isnt converting the gas as it should just same as MOT test, of course they test for HC, Lambda and other things as well but if sensor is good and P0420 is active then mot fail is inevitable on emissions in most cases i would think.

My concern is the new cat is perhaps not up to the job and needing serious heat to switch it active, OE cats are far higher quality and no doubt start working much quicker due to this, also the extra heat shielding on OE cat will help keep it upto temperature as well as protecting things mounted around it, there is no shielding on the cats2u/BM cat and also i currently dont have nappy/undertray fitted on so maybe all this isnt helping with cat dropping out of its zone, if that is the case of course!

Pesky cars

I have a cats2u and I wrap my cat pipes for just that reason.  Almost zero CO at last MOT.

[shnazzle]

Fact of the matter is that if your o2 sensors are all new and working, your cat is new and supposed to be working (whether it's a cats2u or not) and there are no leaks or anything then there is absolutely no reason why your car would throw a P0420.

My original cat was thoroughly knackered, as diagnosed by Steve@D1, and it still passed MOT twice and I never saw a P0420. I then put on a 2nd hand knackered cat with leaking flexis and still didn't see a P0420 until the flexis got much worse after a certain pothole incident on a Dales drive. 

What I mean by P0420 is not an emissions code but a voltage code, is that the voltage may not be reliable for whatever reason; leak, dead sensor, bad wiring, etc.

So either your cat needs sending back, because it's just not up to scratch, or there is an issue that's being overlooked.
How did you check for exhaust leaks? Leaky flexis are not easy to spot. Sprayed soapy water on it? the piece of paper at the end of tweezers test?

[thetyrant]

Its certainly an odd one and can only trust the data that the sensors are working and that cat processing of gasses appears to be intermittent, i also previously had a leaking flexi and flange on the OE cat no P0420 code so not sure how big a leak you need to trigger the code!.

 I think it would need to be a big leak as you found to trigger this code and ive checked the whole system for leaks,  both by ear (which mine seem very sensitive for leaks as proven many times when ive heard peoples leaks and they had no clue), also using the tissue in pliers around the joins and sensors with no movement detected so im confident if there is a leak its tiny and nothing to do with the code in this case. 


We are told the PO420 code is trigged by catalyst not cleaning up the exhaust gases so can only presume that is the case, hopefully its not like the P0125 code that reports as a coolant issue when its actually a pre-cat sensor failure!, sure someone would of figured out if that was the case though

As far as i can ascertain the post cat sensor is looking for less fluctuation in voltage compared to the pre-cat sensors, also wanting to see voltage around the middle of scale it can read so 0.4-0.5v to show cat is working efficiently, how often it checks and what conditions its working with and when it would decide that its not acceptable range etc to throw the code is the unknown, it could be all the time once coolant reads a certain amount but suspect its throttle and revs related as well as of course under high load or no load the engine output is very different, i would guess its at light throttle and above certain revs but below anything to high revs wise, say around 2-4k maybe light to medium throttle once coolant is 90+, my cat seems ok around 3k with voltage fairly steady around 0.5v but between 2-3k can be a little fluctuating so thinking that maybe the issue, it was a lot better last night so will keep an eye on it.

Hopefully its all good now but we will see, i have my doubts.

[thetyrant]

I have a cats2u and I wrap my cat pipes for just that reason.  Almost zero CO at last MOT.

Interesting, ave you seen issues without wrapping them or just belt and braces ?

[Carolyn]

I have a cats2u and I wrap my cat pipes for just that reason.  Almost zero CO at last MOT.

Interesting, ave you seen issues without wrapping them or just belt and braces ?

Belt and braces.  hot cats work best so....

[thetyrant]

Ive been doing some more reading on testing cats and found what was new info to me, basically measuring inlet and outlet temperatures on outside pipework with an infared thermometer is another good guide to proper functioning catalytic converter.

Its not something ive come across but a proper functioning cat should have higher outlet temperature than the inlet by approx 100degrees due to chemical reaction taking place, ive just checked mine after a quick drive out at lunchtime and it was just about bang on that with higher outlet temp so thats promising at least.

Hopefully useful info and its nice easy way to do a basic test if you have a infared thermoeter to hand that can read high enough, mine measured about 180c inlet and 270c outlet which is max of my infared gun, i guess exact number isnt critical its the difference your looking for to confirm reaction is going on inside, if temps is same or close both sides of cat then it aint working!

[shnazzle]

Indeed. There was a video from a popular YouTube mechanic explaining this years and years ago. 
It's definitely effective

[thetyrant]

Havent used the car much this weekend but did bring it into work today (10mile trip), was fine going in nice and smooth with on issues, nipped home at lunch and got the EML on way back in ,  guessing its P0420 again but couldnt be bothered scanning it as i was so annoyed!....not going to mess about anymore and soon as a get chance with get it to mot centre for sniff test see what that shows up!

[thetyrant]

OK swung by my MOT guy yesterday afterwork and after 10minutes of chatting while car sat idling staying warmed up (had just done 10miles drive to get there) we hooked it upto the gas analyser to see what she is putting out.

Sat at idle and fully warmed up straight away it failed on CO as expected with numbers pointing to cat not performing as it should, next we held it at 3000rpm for fast idle test and after about 1 minute of this the cat became active and emissions dropped to as they should be, left it like that for a minute or so and emissions stayed constant at mot pass levels, let it drop it back to idle and stayed good for about 5minutes before emissions then rose again and went back to CO fail level.

So it would pass the MOT as it is providing it doesn't get any worse, but when driving normally/steady its not getting cat hot enough to keep the cat active which is triggering the P0420 code.

MOT guy is a decent bloke and I was lucky to catch him just before closing with no other jobs to get back to so was happy to chew the fat about other possible reasons etc, we discussed intake and exhaust leaks but way it reacts to higher revs and from what he is seeing on analyser he said its scream out as the cat not lighting up until revving it, possible either a small hole/bad seal in cat matrix that is sealing once fully hot or its just a poor cat which only works when properly hot.

I will be giving Cats2U a call when I get a minute see what they have to say.

Below are pictures from the tests, first up sat idling after 10mile drive to warm it up...



And after holding it at 3k rpm for a minute or so...

[1979scotte]

Sounds like it is behaving as if it is a 200 or 100 cell sports cat.

They need a good thrashing before they will pass mot especially the 100. Saying that I had a 200 on my turbo and that never threw a cat code.

[shnazzle]

My 200 throws a p0420. 
Less so without my emanage, so it's quite sensitive to the mixture being just right