I'm having the same problem....It seems to throw the code about once every week. I T-eed into the line that runs from the charcoal canister back to the gas tank, and hooked a vacuum guage to it I could monitor from inside the cabin. It appears that whenever my car is running, it keeps the gas tank under a slight vacuum (by slight, I mean the needle doesn't move much away from zero (less than an inch of mercury)). As another test, I filled up the gas tank super full. Then I hooked a hand vacuum pump up to this same T-eed line. Once I built up about 1-2" Hg of vacuum, I could hear a bubbling in the tank as air reentered the tank somehow. The bubbles sounded like they were coming from where the fill spout vent lines connect to the main gas tank. I'm not sure if this is intended or not. Maybe some kind of vacuum relief so the tank doesn't implode if full engine vacuum is applied? The air is not coming in from the cap, and the cap o-ring is in good shape. Anyway, I'm not sure how this system even works, what numbers I should be getting, or the correct way to diagnose it. Thanks in advance for any help! Sorry I couldn't be of more help, Bruce!

Jason
94 850 turbo wagon, 203k
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Jason S. '94 850 turbo 203k