I own a 2002 Honda civic LX; now its gas gauge has started giving problems. It seems to have a mind of its own; sometimes shows gas is full and after couple of minutes half. What could be going wrong here? Is it a costly repair?
In the repair manuals for the car, not the owner's manual they cover a test of the sensor/sender unit. It is highly possible that you have a shorting wire. Get the manual and test it. I think all you need is a volt/amp meter. But it sounds like either a faulty sensor/sender or a short. The final possibility is the gauge itself.
Costs - I can't address that. Shorts are difficult to find (especially when the weather is cold like it is up here).