Fuel Gauge Woes/P0463
 

The other night as I was on my way home my ‘13 FRS randomly threw a P0463 code as a pending fault. At the time the fuel gauge was reading accurately. This isn’t the first time this car has done this (more on that later). I decided the next day to try and reset it and see if it was a fluke and the CEL would instantly come back on after resetting it multiple times. Then I went to fill it up from 1/3 to full and the gauge stayed at 1/3. Now it’s the next day and the gauge still is at 1/3 and I know for sure the tank is full it took 7 gallons yesterday and I haven’t driven it since.

Now I previously had a very similar issue about 2 years ago and I ended up replacing both sending units along with upgrading the pump and adding the fuel baffle door and the problem went away. But I noticed ever since that occasionally the fuel gauge will only go to 3/4 after filling up when it never used to do that the first year or 2 I owned the car. For the past 2 years I’ve just ignored it as it’s pretty few and far in between when it acts up.

Could this have something to do with running E-85 most of the time? I’ve ready multiple threads saying it’s not an issue but I don’t see why else my sending units would go bad twice in the span of 5 years of ownership. Unless it’s my actual gauge going bad?

For context I’m on a Delicious Tuning flex fuel kit w/ ECUTECK tune, and UEL catless headers. The car has been set up this way since I bought it in 2019 but between 2019 and 2021 the car rarely saw E-85. After moving to CA in 2021 now the car almost exclusively runs on E-85 unless going on a long trip. I’m going to try burning this tank of E-85 and try filling up with 91 to see if that does anything. I also just checked the connectors at the sending units and reseated them and they seem fine.

Odd. I don't have much input on this other than agreeing with what you may have read elsewhere about E85 not being the issue. I don't see how another fuel could cause this, and it has certainly never been reported before that I'm aware of. I also don't anticipate it being the fuel gauge, as the gauge is just a readout and not something that would throw a CEL if it went bad. Just out of curiosity, are you using an OEM sending unit?