I went from using 1/4 tank of gas to get to/from work to using 1/2 tank in less than couple of weeks. It does not sputter, has not lost any power, etc. What could be causing this? Also, once in a while, after starting the car and pulling it into gear it hesitates before engaging. What is the problem?

you need to read the manual for the machine you are hooking to the vehicle .
These are errors not codes you need to understand how it works better.

the whining noise is your engines alternator bearings
they are worn out , the alternator is close to failure
it is barely producing any voltage
( the battery light in the dash only indicates that the alternator is no longer generating any amperage )

Do not understand the fuel problem, but the lights is probably a bad alternator. Major auto parts stores will test it for free

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change the fuel filter for one, this is telling you that your pick up in the tank is getting clogged, I would drop my tank, and drain it, flush it, and check the pump at that time

Does it stick at about half full? I would fill up, the gauge would show full then after 60-70 mile when gauge should show less than half to a 1/4 tank the gauge still showed 1/2 tank so I'd go ahead and fill it up. Finally, I watched my mileage and when my yellow low on gas light came on I filled it half full. After a couple of weeks I filled it up and the gauge has worked every since.

HELLO: It could be a frozen gas line and or stopped up filter, filter is on drivers side under the truck, looks like over sized small coke can with a connection on both ends. Thats the first place I would check.

If I'm understanding you correctly, you believe you got contaminated gas from a station where they had recent work done on their tanks. If that's so, Now that you've run most of the gas out I would start by changing the fuel filter then fill the tank with good gas (I might even go up on grade for this tank). Although it's unlikely you may have gotten a fair amount of dirt or water, you may want to try adding some dry gas in case there is still water in the bottom of your tank.
If the new filter seems to clear the problem but it come back after a short while you'll need to take the tank off and flush it. If you do it yourself don't dump the gas on the ground. If you have to flush your tank you'll need to flush the gas lines and replace the fuel filter again.

fuel pump is going weak

sounds to me you may be out of gas

alot of vehicles start to mis read at 1/4 tank

i would just through some gas in it and try it again

cycle the key on and off a couple of times to prime the fuel system