Hey man,
Try performing this instructions... (if that doesnt work, then you will probably need to swap your level sensor that is inside your tank... i would buy a used one from ebay but original toyota, the new one if you have $$$ would be better, but since you are trying to figure it out, a used one will do the trick... but try to do the steps below first.)
Here's my update (and, as always, I will indicate that many people on this forum know much more than I):
I spent this past summer periodically trying to solve my issue (see my previous post on this strand). Unfortunately, the reset instructions above and the level sensor were not my issue, nor my fix. From my internet research, I concluded that there is a relatively rare but occasional occurrence wherein a single incident with the trailer plug or tail lights creates a short in the wiring that for some reason makes the fuel gauge act with the symptoms you're describing. IF you are lucky enough to find the short/fix the grounding issue, the gauge appears to go back to normal. If you can't locate it, you are out of luck. During the summer, I tried to follow wiring diagrams and systematically test every possible wiring route I could get my hands on with my meter and, when possible, checking and tightening any grounds I could get to. I went through everything I could reasonably get to and found no issues, although on a few occasions, when tightening the grounds, I definitely noticed slight changes in the patterns of "misbehavior" of the fuel gauge, making me think I was on the right track. Further, whenever I plug in my camper to the trailer hookup, the fuel gauge works again.
I never solved it, but after a summer of tons of driving and using the trip odometer to estimate refueling, I decided there was no other negative impacts to what was happening. So, when my buddy told me to my face, "Dude, its time to just let it go", I (a) pulled the dashboard (and replaced the dash lights with LEDs while I was in there) and yanked the low fuel light out; and (b) bought and installed the ScanGauge that others recommended. It creates an additional step when fueling up (i.e. inputting the amount of fuel I put in), but I don't even think about it now and actually much prefer now knowing exactly how much fuel is left, particularly on road trips.
So, if you combine all the advise above (and elsewhere) from folks who know much more than me, and my experiences, you may perhaps follow the steps of:
1. Resetting the sensors as indicated above
2. (optional) Replace the level sensor -- if you suspect it may be the culprit, or just want to eliminate it as a possibility
3. Check and potentially replace the tail light bulbs (this worked for at least one other person with the exact same issue...an old bulb was creating a short).
4. Check the grounds on the trailer wiring, tail lights, and perhaps elsewhere.
5. Give up, yank the fuel light out from the dash and install a ScanGauge.
Good luck and let us know if what works, if anything! I know several folks around the web are still searching for the solution to this rare but frustrating mystery!
