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My gas tank is possessed by deamons!

I am hoping that you guys could help me out. I have a 2000 Subaru Impreza with 190,000 miles. The car has only had a few problems in the past. Recently when I get a full tank of gas something strange happens. About an hour after filling up the gas gauge will go down to read empty, and the light will come on showing that the tank is empty. The check engine light will also go on. After about 2 minutes the gas gauge will go back to normal, and the check engine light will go off after about a day. My mechanic checked the computer and found nothing wrong. The car runs fine except for this problem. Anyone have any ideas?

I had the same problem with my 2006 Chevrolet Uplander minivan. It turned out to be the sending unit in the gas tank. Fortunately, my vehicle was under warranty at the time.

I don’t know why this condition sets off the check engine light, but it did. The code that was stored pointed right to the sending unit.

There’s a bad spot on the sending unit.

My mercedes does a similar thing. You have a bad sending unit in the fuel tank. My tank has two units and I have to drop the axle to get the tank out. So I live with it and use the odometer when the gauge is off. At least for me the gauge mostly does this only on long 1+ hour drives. I can live with it. At this point I would suggest not worrying about it the cost may exceed the value to replace the unit. Just enjoy the car.

“I don’t know why this condition sets off the check engine light, but it did.”

My guess is the computer expects the voltage from the sender to be within a certain range from empty to full.
When the sender malfunctions it goes beyond this range, probably zero volts.
Many sensors are designed to not include zero in their normal range.

Running out of gas can be damaging to the cat converter, so the gas gauge is an important part of the emissions control system.

If you ignore the problem you run a small risk of another problem cropping up un-noticed while the check engine light is already on.