Working Fuel gauge but not reading on screen

I bought my outlander from an Older man that never rode it. It has 400 miles and it looks brand new. It is an 08 i have done some research on here and found out that this is a common problem but my question is how to fix it. i put a hanger down in the gas tank and hooked it onto the float and lifted up and the fuel gauge went right to full. but if i fill the tank up the gauge will say its empty. why doesnt it work with fuel but will work with a hanger when being pulled up.

Working Fuel gauge but not reading on screen

I bought my outlander from an Older man that never rode it. It has 400 miles and it looks brand new. It is an 08 i have done some research on here and found out that this is a common problem but my question is how to fix it. i put a hanger down in the gas tank and hooked it onto the float and lifted up and the fuel gauge went right to full. but if i fill the tank up the gauge will say its empty. why doesnt it work with fuel but will work with a hanger when being pulled up.