hi can any one tell me if there is any one that has got to the bottom of fault code po420 cat effiency bank 1 below effiency,i have seen various threads about this but have never seen any that have actually fixed the problem ,no performance problems standard cat exhaust etc just the eml on every few days,skoda tech are saying cat problem but this car has only covered 60k miles and the fault has been documented for the last 4 years from 25k miles and i can not believe vw group make a cat that only lasts 25k miles ,any help on this would be great there must be someone out there that has fixed this problem thanks rpa repairs

Has the car got a air leak somewhere as this would upset the sensors and throw a engine warning light,

My old 2.0t volvo s40 used to put a similar fault code in but only because it didnt actually have a cat

Maybe the car has had some contaminated petrol at some point in it's life. Remember that batch of silicone-contaminated petrol from Tesco's? It may have been something like that.

Maybe the car has had some contaminated petrol at some point in it's life. Remember that batch of silicone-contaminated petrol from Tesco's? It may have been something like that.

can not find any more air leaks have replaced various hoses under the manifold and on the over complicated vacume system, skoda tech advised me of the same fault on another car last week they replaced all the hoses inc the servo pipe then replaced both o2 sensors then the cat which seemed to cure the problem all at the customers expense of over £1000 . :'(

I get this code but its only because of the high flow cat i have. It could be that the 02 sensor needs replacing. my impreza had this problem and i fitted a new one and never had any more problems

I get this code but its only because of the high flow cat i have. It could be that the 02 sensor needs replacing. my impreza had this problem and i fitted a new one and never had any more problems

Think i will have to take the plunge and replace the sensors first as far as standard cat or high flow cat fitted the warning should not come up should it ? surley thats why people put high flow cats on to keep the management system happy or we would just all fit de-cat pipes?

Does everyone who has a highflow cat have the eml light on all the time ? was thinking about this mod but if the eml is on all the time i will not bother.

No i dont always get it. I find if ive been caning the car then it comes up but i've got a code reader that clears the code so its no big deal. Its pureley the fact that theres less restrictions in a high flow hence the flow of exhaust is erm..... higher and the sensor throws a wobbly

have a high flow milltek downpipe and cat and have never had the light on,mybe a dodgy o2 sensor or the cat is begining to break up

also bank 1 is before the cat isnt it?

I Had a bank 1 too rich fault in mine can't remember p code. I switched from supermarket fuel to shell v power and runs like a dream now and I not seen fault again