Ok, I have a 1995 honda civic ex with the 1.6 liter engine. A while ago the fuel gauge started showing full intermittently when it wasn't. Eventually it stuck there. I tested the sending unit, which is fine, so bought a gauge from the junk yard. Had the same issue so bought a brand-new one. Same thing. Finally broke out the volt meter and checked it. Instead of the 5 to 8 volts it should be, its 12 to 14 volts. Haven't changed any wiring or added anything, so not sure what is causing it. Any insight would be much appreciated.

 

Where are you measuring with the volt meter?

 

If the wire between the gauge and the tank shorts to ground, it will falsely read full.

 

measuring at the sending unit

 

The gauge head may not be grounded. The three screws on the back of the gauge are ignition power, wire to the tank, and ground. With the wire to the tank open, the needle should go to less than empty when the key is turned on. Test the voltages on the back of the gauge with the cluster pulled out of the dash but still plugged in.

 

Ok, here are some new details. Measured the voltage at the sending unit, got 12 to 14 volts. Took the cluster out, and measured at the gauge. Between the positive and negative, had 12 to 14 volts. Between negative and the F connection i had 5 volts. Cut the power and checked resistance between F and negative and had what i should for what gas is in the tank. Then checked between positive and negative and had 0 resistance, so is a short somewhere. When I took the wires loose from the cluster, and checked again i had resistance between positive and negative, so isn't the gauge. Any new ideas?

 

You can only measure ohms while the circuit is completely dead. If you see a negative reading on an ohms test, that means there is some residual voltage messing up the reading.

Unplug the cluster and measure the resistance to ground through the sender, do this at both the dash end and the tank end of the wire.

With sender circuit disconnected and key on, gauge should read below E.