B8.0 differs from B8.5 in the fuel pump wiring. Your profile at least mentions 2013, so B8.5.
The two fuel level sensors are wired to the instrument cluster. The sensor 1 on the in-tank pump (front right, under the rear seat bench) reads the lower 3/4 of the tank, the sensor 2 on the in-tank vent unit (left rear, under the cargo floor, have to cut the panel to access) reads the upper 3/8 of the tank. The instrument cluster transitions from sensor 2 to sensor 1 in the 6/8 to 5/8 portion of the tank.
Each sensor is just a poteniometer swiveled by the float arm. The wiring for each sensor passes through the in-tank pump connections. For the B8.5, they are all on a single plug, the 6-pin 2x3 plug.
To test the sensor 1 with a multimeter in resistance measurement mode, unplug the 6-pin plug and test the contact pins on the pump flange:
Connect multimeter (resistance test) between contacts -2- and -4-.
Tank empty: approx. 280 Ω.
Tank full: approx. 65 Ω.
Connect multimeter (resistance test) between contacts -2- and -6-.
Tank empty: approx. 60 Ω.
Tank full: approx. 275 Ω.
Connect multimeter (resistance test) between contacts -4- and -6-.
Sender in any position: approx. 340 Ω.
And for sensor 2:
Connect multimeter (resistance test) between contacts -2- and -3-.
Tank empty: approx. 290 Ω.
Tank full: approx. 45 Ω.
Connect multimeter (resistance test) between contacts -2- and -5-.
Tank empty: approx. 50 Ω.
Tank full: approx. 295 Ω.
Connect multimeter (resistance test) between contacts -3- and -5-.
Sender in any position: approx. 340 Ω.
Also note:
To obtain an exact measurement of the resistance value for the specification Tank full, the fuel tank must be completely full. For this, drive for at least 500 meters after filling the tank to let air bubbles escape from the fuel tank; then add fuel again.
It could well be a wiring issue from the 6-pin harness plug to the instrument cluster plug as well. Or an internal fault in the instrument cluster circuitry. But start with testing the sensor to see if it's obviously the issue or not obviously the issue. Could be an issue with the wiring from the sensor 2 to the backside of that plug on the in-tank flange as well.
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