2001 VW Jetta 1.8L Turbo P0420 code

My 2001 VW Jetta with a 1.8L Turbo recently had the "check engine" light come on. I've read the stored codes and they were P0420 "Catalyst Effeciency Below Threshhold Bank 1" and P0171 "System Too Lean Bank 1". Is it possible that the two are related or that one problem causes the other? The car has 112k miles and runs well, though I've noticed some lag in pick-up. Any help is appreciated.

it's probable

Hi there. I think most of the time the p0420 code indicates a faulty catalytic which might cost you a few bucks. As for the other code, well it seems that you either have a vacuum leak somewhere and your car is breathing too much air or it might be that the catalytic is playing tricks on your 02 sensors. I would start with the catalytic and check for vacuum leaks at the same time. When opening hood, you see a big piece of the intake, right underneath there is a bracket that holds a few vacuum lines, might wanna take a glance there !

Hope this helps

Carlitos30

I wonder If you can help me also I have a 2002 1.8T Jetta with above fault code P0420 - catalyst system, bank 1 efficiency below threshold. Now bear with me here so far we have changed on the advice of our local VW Dealer Air hoses, Air mass Sensor, Lambda Sensors Both, and I’m sure probably totally unrelated the thermostat!
Now we have the emission light on yet again and this they tell me it is telling them P0420 - catalyst system, bank 1 efficiency below threshold they have checked the Cat' and it is testing fine they have also checked the wiring in case there is a loose connection now they are telling me i need to shell out $1,100 for a new Cat now I'm confused how can they tell me on Monday the cat is fine and now they are saying replace the cat?????? have had the car back and so far no emission light after 5 days and 800 miles!
Also they are telling that there computer systems are showing a technical bulletin: 26-05-02 - that may be applicable in this case but here’s the thing we are stationed here in the UK with the US armed forces UK VW dealers apparently can’t see US technical bulletins can anyone please help!

HI there ! As per my first comment, changing the Catalytic is normaly the first thing to do since they usualy go faulty after a few years. In some rare cases, vacuum leaks and faulty MAF sensor or Mass Airflow Meter sensor can also cause a P0420. Not sure why they would replace all those parts and then simply say , Oh its your catalytic, If I were you I would have them re-install all my old parts since they made no difference from what I can see. Now, its true, there is a Recall on some cats but not all models. From what I know, recall applies to 2001 models (1.8T). The thing is that they mistakenly installed a single brick instead of a double brick catalytic and so the recall is to replace the single by a double but if your vehicul is a 2001 and is already a double, then the recall does not apply, but if its a single then dealer should replace no questions asked. As for yours, well you have a 2002 so i don't think it applies, if you wanna make sure, I would call a dealer anywhere in US or Canada and explain to them that you need to know if there are any recalls do be done on your vehicul, have your serial # ready......if there are, ask them if you can have the recall done in Europe, they might either give you another number to call or will tell you to have it done, keep you receipt and have it re-imbursed when you get back to the states. That would be your best bet but I think catalytics on some vehicules have a warranty of 8 years or 160 000km, so I would ask the US dealer about that aswel.

Good luck and let me know how it goes !