VW Passat P0431

Tiny
DDCYR40
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  • VOLKSWAGEN
Hi, I've got a 2000 VW Passat V6 and was traveling on the highway for a half hour or so and the check engine light came on, and scanned and said P0431, which is Warm Up Catalyst Efficiency Below Threshold (bank 2). Just last night, I drove again on the highway for an hour or so, and it was obvious by watching the gas gauge that I was getting worse gas mileage. I cleared the code and went and drove a half mile or so and no code came back up. Any idea what this is, and if it is going to stay off? Thanks
Saturday, February 10th, 2007 AT 2:30 PM

5 Replies

Tiny
CARUNDELL
  • MECHANIC
  • 602 POSTS
Hey Doug,
Let me reassure you that this code/issue has absolutely nothing to do with fuel economy! It's strictly an emissions issue. The code your getting is a result of the PCM monitoring the Downstream O2, that O2 "tells" the PCM if the bank 2 catalytic converter is treating the exhaust gases effectively and to spec.
To answer your question, you did what a majority of techs would do, as in clearing out the code and seeing if it re-occurs. Which is also what I would recommend to do! It will take some driving time for the OBDII monitors to set, but if the check engine light illuminates again and the same code pops up then repost here and we can help with further diagnosis! Let us know!

Chris
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Monday, March 5th, 2007 AT 3:16 AM
Tiny
DDCYR40
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I actually drove the car for say 400 miles or so, with 300 or so highway speeds, and it came back on. I didn't check the code, but I am assuming it is the same code. I left the car home, and went back to school with my girlfriend so I didn't have to deal with it. And I know for a fact I received worse gas mileage with the light on. I dunno if it was a coincidence, but I am positive because on the highway, I typically get around 25, and I was getting 18-19. Let me know, I won't be able to check the code for 3 weeks, but if it is the same code again, what do you suggest? Thanks a lot.
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Monday, March 5th, 2007 AT 10:11 AM
Tiny
CARUNDELL
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Hey Doug,
If your certain that the fuel economy has decreased than there may be a coincidental issue. But the cat efficiency code is not the cause. Let me know what you find when you get it re-scanned!

Chris
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Monday, March 5th, 2007 AT 11:55 AM
Tiny
DDCYR40
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With the possible problem you said with the cat, would that be the actual cat not performing properly, or the downstream o2 sensor for that cat malfunctioning?
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Monday, March 5th, 2007 AT 2:26 PM
Tiny
DDCYR40
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Checked the codes, same code came up with its partner code, p0421, how would both go bad at the same time? Help me out
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Saturday, March 24th, 2007 AT 9:47 PM

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