billjax

2002 A4, Blackwing, Z06 catback, 42K miles.

Checkk engine light came on while driving and the above code was set: P0420HC - TWC System Low Effeciency Bank 1

If anyone could provide additional info, I would sure appreciate it!!

More background info:

Check engine light came on last week, first time ever. Took it to dealer and tech said they found "misc. misfire" codes and cleaned the injectors. I didn't think to ask what the actual codes were.

Couple of days later, the CE light came on again, so I hopped on CF and got the info on how to read codes and reset them (yes, I should have done this in the first place...).

P0420 was set as well as a bunch of other ones, which I did write down. I wasn't sure if they were left over from the dealer so I cleared everything. I then drove the car and in about 10 minutes, the CE light came on. Got home, read codes and P0420 was the only one set.
P0420 OBD Trouble Code

Some google info:

Technical DescriptionCatalyst System Efficiency Below Threshold (Bank 1)

What does that mean?Basically this means that the oxygen sensor downstream (after) the catalytic converter on bank 1 is detecting that the converter is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

SymptomsYou will likely not notice any drivability problems, although there may be symptoms.

Causes A code P0420 may mean that one or more of the following has happened:

Leaded fuel was used where unleaded was called for
An oxygen sensor is not reading (functioning) properly
The engine coolant temperature sensor is not working properly
Damaged exhaust manifold / catalytic converter / exhaust pipe
Retarded spark timing

Anybody had any of these??

trussme

...means your "Bank 1 Cat. Efficiency is not meeting threshold requirements of the PCM" (not acceptable to the computer) 02 sensor can't read it...I had this code after Kooks LT headers & hiflo cats installed on my P1-SC-1 charged LS1...now's the time to install a pair of 02 Simulators and be done with it (as I did) I spent 100 bucks on mine, they took 25 minutes to put in (in place of the left & right 02 sensor cables)...you will soon probably get the "brother" P0430 code("Bank2") ...it is possible to tune them out, but 02 Simms, will stop these codes from throwing the CheckEngine light at you ...

billjax

Thanks for the reply. I have stock headers - just Z06 catbacks I put on several years ago. Could one of the stock 02 sensors be going bad?

dpd

no.you probably have a bad cat.

trussme

"replace cat(s) or install 02 simms"....

BadAV

I agree; it's probably the converter. Take it to the dealer and have them check it. If it's bad it should be replaced at no cost under warranty.

billjax

Thanks again for the replies.

I'm calling the dealer tomorrow to get it checked out. If I read the warranty booklet correctly, if the cat is bad, it's covered as is labor and diagnostics. I'm past the two years for the 02 sensor, if it turns out to be bad, but my GMPP Major Guard doesn't specifically exclude it so hopefully I'm covered there. We shall see...

I'll post news as I get it!

dpd

emission stuff is 5/50[years/miles],the pcm,tac,cats are 8/80.both are federal law no matter where you live.this is 1 to thank the carb ****'s for.they are the ones who cranked on the manufactures to cover this stuff for that kind of time period.