Guys this is from another thread I just posted to but it relates to this one I think. It had a max capacity of 254 Liters you could enter but since my tank is only 32g. I put in 121 Liters.
Theres a few threads on this matter which I have posted on about using AlphaOBD app to recalibrate the CLUSTER readings of the gauge to coincide with actual fuel level.
Like others my fuel light would come on @ 50 mile range. When I would fill it would only take 26. At most it took 29 and that was with the gauge on E hard for 25+ miles. My 2018 CTDHO truck has the 32 gal tank.
So I went into the Body module using ALPHAOBD and changed some settings. One thing was the capacity to 121 liters (32 g) . I also changed the Cluster Calibration percentage readings for FULL, LFW, & EMPTY to the highest for full, and lowest for empty and the LFW I think I set to 2 or 5%.
I ran a test initially after the recal. I filled the tank and ran it down to 1/4 tank on the gauge. Upon filling, from 1/4 to half it took 8.2 gallons. I continued to fill to half and it took another 8 gallons. The to full it took another 8. Since it's a 32 gallon tank it looked pretty promising my gauge is accurate.
Final test I ran it empty yesterday. the 50 mile range light came on with the needle in the red. I continued to run it until the needle was down to E and range wouldn't give miles anymore. I filled the tank yesterday morning and sure enough the pump clicked off at 31.7 gallons with me able to top it off with 32.2 gallons. I don't normally top off but I wanted to see how much more I could squeeze in.
Conclusion problem solved for me. I'm going to run this tank low again and see if it has the same results.