My 2017 Equinox LTZ has a peculiar problem with the fuel gauge, to only works from full to half full, at a quarter tank takes 40 liters or 10.5 gallons, doesn't effect the operation, just wondering if it is possible to calculate to full scale.

 

No calibration possible. There are two fuel level sensors, one on each side. The two are averaged by the BCM to derive current level. Sounds like one of them is failing. I recently had a pump and sensor replaced, total cost was $800, the sensor can be replaced separately.