2003 VW GTI - OBDII Code P0421

I am the owner of an '03 GTI 1.8T with just over 94k miles. The check engine light has been popping up every now and then over the past few months. I am hoping someone here might be able to help me out.

First time the CEL came on, I took it to my local mechanic, who pulled the code and reset it for me, just to see if it would come back. The CEL came back a couple hundred miles later. Second time, I took it to AutoZone to have the code read myself - they pulled P0421.

OBDII code P0421: "The PCM has determined that the warm up catalyst efficiency for bank 1 is below threshold for the current engine operating conditions."

I had AutoZone reset the code as well. Now, the CEL came on again this morning after another few hundred miles of driving with it off (and a few cold morning starts here in NJ).

I've done a bit of research and I think I have the problem narrowed down to two possibilities:

1.) The second O2 sensor (downstream of the cat) is dirty or going bad, the computer is interpreting this as a low cat efficiency reading, and the O2 sensor needs to be cleaned or replaced. 2.) The catalytic converter really is going bad and needs to be replaced.

I was leaning towards a dirty/bad O2 sensor, because the CEL takes awhile to light up after it is reset. My thinking was that if the cat really was running at low efficiency, the CEL would come on much more quickly. A dirty or bad O2 sensor might throw a funky voltage at the computer only every once in awhile.

Also, the car passed inspection two weeks ago.

Am I on the right track here? How do I fix this? I'm in the midst of trying to sell the car and I don't want to have any issues with the CEL once the car is out of my hands.

Reply to
rtb1119
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look no further... you got a failing cat which maybe covered by warranty. Ask your dealer.

Reply to
Lost In Space/Woodchuck

Had AutoZone scan it last night - P0420 "cat efficiency low"

VW provides an 8 yr./80,000 mi. emissions warranty so I'm not covered - but I found a shop that will install a generic cat for me for about $240.

Thanks for your help.

messagenews: snipped-for-privacy@l12g2000cwl.googlegroups.com...

Reply to
rtb1119

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