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The gas cap on my 2003 Pontiac Vibe used to make a slight sound of "pssstt..", the sound of some air either entering or exiting from the tank as I was opening the cap.

Two months ago, the gas cap stopped making that sound when I unscrew it to fuel, even though I still tighten it quite firmly after fueling.

At just about the same time, the "check engine" light has gone up. The OBD reader says that the "catalytic converter bank one sensor" is faulty. But before I replace it, I want to clean the gas cap thoroughly to rule out that the coincidence of the lack of air release sound and the check engine light is not just a coincidence but rather a cause and effect.

I see here instructions for cleaning the gas cap. In summary:

  1. Clean the metal part (the top of the gas tank intake) with a "petroleum-based lube".
  2. Cover the rubber seal on the gas cap with a "silicon-based spray" to prevent the petroleum-based lube from deteriorating the rubber.

Are these instructions accurate?

I'll throw in a silly question: Would Vaseline-brand 100% pure petroleum jelly (the one used for baby diaper rash) be a suitable "petroleum-based lube" or is a car-specific product needed?

And if I use a 100% cotton fabric to clean the top of the gas tank, does this suffice to minimize the chance that I'll generate a spark that blows the tank on me?

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    The gas cap is not related to your CEL – Zaid Sep 29 '15 at 18:01
  • @Zaid What's a CEL? – Calaf Sep 29 '15 at 18:30
  • Check Engine Light – Zaid Sep 29 '15 at 18:56
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Are these instructions accurate?

These instructions sound accurate to me.

Would Vaseline-brand 100% pure petroleum jelly (the one used for baby diaper rash) be a suitable "petroleum-based lube" or is a car-specific product needed?

Absolutely.

And if I use a 100% cotton fabric to clean the top of the gas tank, does this suffice to minimize the chance that I'll generate a spark that blows the tank on me?

It should be fine.

With all of that said, plan on replacing the gas cap whether this cures your ill or not. It sounds like the seal is worn out and just barely doing the job. Cleaning the seal is usually only a temporary fix.

Realistically, @Zaid is spot on. This is not the cause of your CEL. I personally have no issues with going the least expensive and least time consuming route first, then following up with the rest. In this case you'll most certainly find your CEL will not go away and you'll end up replacing the O2 or the converter.

  • Sounds reasonable.. but what the O2? And when you say "the converter", you mean that sensor, not the actual converter. Is that right? The actual catalytic converter is made of ceramic, if I understand correctly, and so it should be rather hard wearing. – Calaf Sep 30 '15 at 1:05
  • O2 = Lambda sensor = oxygen sensor. That would be the one at the catalytic converter. Converter is the catalytic converter. It doesn't matter what it's made of, they can still go bad. – Pᴀᴜʟsᴛᴇʀ2 Sep 30 '15 at 1:35
  • I'm still wondering.. If the gas cap makes some release sound (air pressure adjustment) at every tank refill for ten years, and then one day it stops making that sound, wouldn't you also wonder if that by itself is a sign that something has gone wrong, aside from the check-engine-light? – Calaf Sep 30 '15 at 15:34
  • That's what I'm trying to tell you ... replace the cap. If it isn't bad now, it will soon be registering as bad in the near future. – Pᴀᴜʟsᴛᴇʀ2 Sep 30 '15 at 18:31

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