I have an 08 G35 journey sedan.
When the low fuel warming light comes on and I fill up, the car takes between 9 and 11 gallons. On the last tank, the car went 220 miles and took 11 gallons. So it looks to me like the gas gage is reading empty when there is still 8-9 gallons in the tank. What could be causing this problem, and is it something I can fix myself?

Its replacing the fuel sending units. If you can get a manual you can do it yourself. The units are around 200 a piece and you have to figure out which one is bad. I think theres 2? Ive had this issue for a year now I pretty much live with it I just look at the trip meter to gauge when Im filling up.

I can easily get to the sending units under the rear seat.
I have volt meters and ohm meters.
Does anyone know how I can test each sending unit?

I pulled both sending units and measured them with an ohm meter. Both sending units have varying resistance as the float is moved.
I don't think the sending units are bad. Last night when I pulled the right side, where the fuel pump is, the tank was at least half full, and the information on the dash said 41 miles to empty.
What else could be causing this error? Is there any other kind of troubleshooting I can do?

Did you ever find a fix for this issue? Im going through the same thing now

the units are bad and they need replaced. they are very very easy to replace and you cant get them for
200$ total on courtesy nissan parts.

cleaning them might work but its not full proof. you need to cop up the 200$ total and just replace them. takes less than an hour with basic hand tools.

I cleaned my fuel sending units before it read 3/4 full but after cleaning it now reads FULL but I can only put 10 gallons the same as him.

I TESTED BOTH OF THEM WITH THE OHM READER AND IT TESTED GOOD..thats the part that throws me off.
How can it test good when the flap is fully up and fully down it gets the correct reading on both of them...BUTS ITS BAD????

Mine drives me nuts - if I drive it till the light comes on it still has 4 gallons left. Never have put much more than 16 in ever. My '05 did the same thing...

You do realize that the normal factory calibration is to show 0 miles of driving range when you still have 2.5 to 3 gallons left, right? The extra gas is considered your "reserve" and is supposed to save you from inadvertently running out of gas. You will find the same on pretty much any car out there.

Gas guages used to read true, but people kept running out of gas. Now that it reads E earlier there is much less issues lol.

Yep, back in the good ol' days when people were also taught to routinely scan their gauges as a basic part of driving skills/requirements. Nowadays, and probably due to the introduction of computers into automobiles in general, people just drive without a glance or thought until some big flashing light finally distracts them enough to notice something is amiss. In general, modern cars are vastly more reliable, and largely because of those computers, but it is sad that, consequently, people never really learn how to operate their machine anymore; they just let the computer do it for them.