It is helpful to have an understanding of the operating principals of a fuel gauge when looking for signs of a fuel gauge problem. The gauge itself gets 12 volts from the instrument gauges fuse in the fuse block. It has a black ground wire that is grounded to the frame and a sender wire. The sender wire extends to the fuel sending unit in the fuel tank. The 12 volts runs through the gauge and back through the sending unit wire, through the sending unit and to ground. The sending unit has a float attached to a rod.
As the float rises or lowers with the level of fuel it moves a small copper brush across a potentiometer board. When this brush moves up as in a full tank, the resistance to ground is less and the fuel gauge rises toward full. When the resistance decreases a higher voltage will pass through the potentiometer to the ground at the tank. Conversely, as the float is lowered more resistance is exerted causing less voltage to pass to ground causing the gauge to lower.
This being the case, if the gauge fails to function completely, loss of power, a bad ground at the tank or a sending unit is at fault. Another problem, believe it or not, is the vehicle has all but run out of gas! Yes, it is a humorous situation but happens often.
If the gauge is very slow to react, the sending unit is bent or the float has a leak and does not rise well in the fuel. If the fuel gauge is inaccurate there is a problem with the sending unit potentiometer and it needs to be replaced. If the gauge stays on full or in one spot on the gauge there is a problem with either the ground at the tank, sending unit or the gauge itself.
Fuel gauge troubleshooting comes down to checking out a few basic components in the fuel gauge. |
Before you get started with fuel pressure gauge repair, you should understand a few things about your fuel pressure gauge. Do you need two of them? Find out before you start working. |
