DTC: P0172 System too Rich on '01 Jetta 1.8T

2001 Jetta 2001 1.8T 58k miles
Just scanned my car because of a CE light on the last four days. Registered with a P0172 System too Rich (Bank 1) DTC. It registered as
both a TROUBLE CODE and as FREEZE FRAME code.
We've been experiencing frigid temps for three weeks here in Seattle (34F or lower) and that's when the CE light started. It's worth noting this is very unseasonably cold.
Some questions for those of you with experience: -- is a "System too rich" condition typically indicative of a faulty O2 sensor (an instrumentation failure) or condition that cascades from a fault in another sensor or component (perhaps fuel injection system)? -- if it is a true rich mixture condition, is it something that might be caused by the type of gas I use? -- do low temps or extreme temp differentials typically accelerate the failure of an already failing O2 sensor? -- should I wait for 40 warm up cycles to pass to see if the DTC clears? -- if it doesn't clear and I let the condition go, what are the ramifications of a continuous rich fuel mixture (if indeed it is a true condition and not an instrumentation problem aka false error condition)?
I'm not too cheap to buy a replacement O2 sensor (a $90 cost) -- is it a DIY job for someone technically inclined? Thanks for any thoughts and speculation.
Mike Seattle
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It's not the O2 sensor! Can your scanner get the data in block value 08 and then display 032? Let me know what the numbers are.
Possible causes 1- vacuum leak 2- bad MAF 3- partly plugged snow screen. 4- it's not the gas
I'm heading for bed or I would continue...
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I used one of the scanners that Shuck's Auto lets you use for free in their parking lot. It's an AutoXRay EZ-READ 2000 and apparently doesn't support more granular reporting than the P code.
I did see a previous post of yours (woodchuck) about 95% of the time a too rich/lean fault being a vaccuum leak. I will check vaccuum connections tomorrow. I have not cleared the code but might go back and clear it and see if the CE light comes back.
Thanks again.
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I had the same code on a 96 Volvo 850 and it turned out to be a vacuum leak. I'd guess with the cold a marginal hose may have cracked.

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Thanks for your help! I'll post the final results as soon as I check the vac hose and reset the code.
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The hoses that are prone to leak/crack are the ones under the intake near number 3 & 4 cylinders. Usually a sign of leakage is if the hoses have some oily build up.

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I checked the vacuum hoses this morning -- no apparent signs of leakage. I cleared the code this morning and will monitor to see if it comes back on. So far so good... If there is a true problem the CE light will re-illuminate, right?
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YES.

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No recurrence of the CE light since clearing the code. Assume I'm out of the woods for now.
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Hi Mike,
Let me know if after you cleared DTC, you are really get rid of the problem. I have same p0172 code on my 98 VW beetle 58K. I just clear the code hoping it is just malfuction. I know that MIL will be activated after 2 drive cycles. You cleared your DTC on 16 and post message that check engine light fine on 18, it is only 2 days and you may not went through 2 drive cycles. Hope to hear from you. check this page: http://www.v8sho.com/SHO/TSB0197HO2SServiceTips.htm
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