This is a typical fuel level sensor.



The three parts are the float, the actuator rod (sometimes called the fulcrum arm) and the rheostat.



As best I can tell the fuel gauge and the rheostat form a voltage divider network. The position
of the rheostat determines the current through the fuel gauge. When the tank is full the float
is high. When the float is high the rheostat resistance is low. When the resistance is low the
current is high. When the current is high the gauge reads FULL. On my 2001 Tracker the
rheostat voltage is simultaneously sent to the PCM.



I can monitor the rheostat voltage by back-probing connector C1 of the PCM harness (pin-12 for the 2.5L engine,
pin-28 for the 1.6L and 2.0L engines).




When my fuel gauge reads "F", the voltage across the rheostat is only 0.42 volts. The computer interprets that voltage as the tank 92% full.



At the half-full mark the rheostat voltage is 2.61 volts. The computer sees that as 47% full.




With the gauge on "E" the rheostat voltage is 4.86 volts with a computer reading of only 1% full.



Both Chevy and Suzuki manuals show a fuel level sensor rheostat resistance range of 3 to 120 Ω.

The PCM only needs to know the fuel tank level for EVAP testing. EVAP leak testing (P0440 and P0455)
is only performed when the fuel tank level is less than 75%. The PCM will only run the fuel tank pressure
(FTP) sensor performance diagnostic (P0451) when the fuel tank level is between 25% and 75%.

 

The 20-amp IG fuse feeds 12 volts to the fuel gauge any time the key is ON.


One of the two fuel level sensor Diagnostic Trouble Codes (DTCs), P0463 sets if the fuel level
sensor input circuit voltage is more than a specified value.


The voltage at the top of the rheostat is fed to connector C1 Pin 12 of the PCM.


Step four of the flowchart says to open connector C401 and look for 7-8 volts on pin 4.


This is where the flowchart looks for 7-8 volts.

 

If the voltage is not between 7 and 8 volts, step 7 checks for a voltage that's too high.


Step 10 checks for a voltage too low. In either case the 7 to 8 volts is derived from the 12 volts applied to the fuel gauge.


The other related DTC (P0461) calculates the accuracy of the fuel level sensor. It does this by
using the fuel injector activity to estimate the volume of fuel used. It integrates the rate of
fuel consumption with the PCM's internal clock. It then compares that calculated change in fuel
volume with the measured change in fuel volume from the fuel level sensor. If the two don't
agree P0461 is set.

 

THANK YOU .

This is all very helpful, I downloaded the shop manual but can never seem to find the good stuff like this .

I'm going to my Sweet's house for Christmas, I'll hopefully be able to convince my printer there to print all this out, I prefer to work from "Cheat /Sheets" whenever I can .