How to check fuel guage. on 2000 Buick LeSabre

Guage reads full most of the time. Ocassionaly will go to empty when tank is low. I removed the harness in the trunk from the sending unit @ gauge still reads full with ignition switch is on.

Asked by for the 2000 Buick LeSabre
1 answer
Likely the fuel tank guage sensor is faulty. With it unpluged from tank unit it is normal for the dash guage to go to full or past full. The wire to the guage unit when its grounded the dash guage would go to empty.