For the last few weeks I've been getting p0420 codes.

I've replaced the pre-cat o2 sensor - so I don't think I'm looking at a bad sensor.

I have a registered version of vagcom - are there any measurement blocks that I can log that might help me diagnose this problem?

Could a leaky turbo or leaky oil lines cause such a problem?

I'm wondering if I should take the car someplace to have the exhaust 'sniffed' (a state inspection facility).

Any help or advise would be appreciated.

Thanks!

 

what does 0420 code say it is?

 

Well post-cat is the sensor that measures efficiency, so you could try replacing it too. As long as the misfires are gone from before you had, it could maybe be that aftermarket cat you have too.

 

if you have an aftermarket cat and no tune... you are going to throw code's no matter what

 

No tune?? I guess you mean something other than a tune up (plugs, gapping, wires, etc).

 

Really? Salesman/mechanic (not my regular mechanic) said something different. He said bank 1 was top one (pre-cat) and bank 2 was the other one (presumably post-cat). I guess either of us could have been wrong or misunderstanding something.

OK - so where is the post-cat sensor? Down below in some hard to reach place? (Even that top one was kind of hard to apply torque to).

 

no i mean tune, like giac apr uni.... they can right out the code for something like that


and the second sensor you will probably need to get from under the car... just follow the wire back to the other side of the car....

 

[QUOTE=turbo kraut;1198336]no i mean tune, like giac apr uni.... they can right out the code for something like that
QUOTE]

Hmmm - sounds like another reason to chip - as long as the car passes the inevitable sniff test. (Only 2 county's in PA require an emissions inspection and I live in one of them).

 

The "bank" refers to what set of cylinders, for a 4 cylinder engine there is only 1 bank, but for a 6 cylinder + there are two or more "banks". Then it is broken down into bank 1 sensor 1 and bank 1 sensor 2 for example (and 2 sensors for each bank, sometimes more). Sensor 1, or the "upstream" sensor is for measuring fuel mixture for the engine, sensor 2 or the "downstream" sensor is used for measuring emissions, and determines whether or not your cat or engine is running efficient enough. Sensor 1 is located before the cat and sensor 2 is located after the cat. The post cat sensor is further back and I dont think it is visible from the engine compartment. Eitherway, it is probably the aftermarket cat that is causing that.

 

thanks. That all seems reasonable and helpful.

So - time to pay for a sniff test. If I pass it, then I don't worry about the codes and maybe think about a tune.

It seems the upsides to a tune are fun! and it might get rid of error codes. downsides are cost/labor to upgrade, more expensive fuel required, and more ongoing maint.

Am I missing anything?