I had my battery changed last week. My gas gauge would tell me that my tank was 3/4's full after I filled up. Now it's telling me it's half full after a fill up. Is this an electrical problem or is there a sensor off? If so, how much are we looking at to get it fixed?Whenever I fill up my car, the gas gauge will say it is half full?Well in order for you to understand how the gauge works I have to explain a couple of things. The fuel pump inside the gas tank does a couple of things. Number one, it pumps fuel to the engine so that it can run. Two, there is what's called a sending unit on the pump. This sending unit is what tells you how much fuel is left in the tank. Have you ever taken a lid off the top of a toilet? It's basically the same idea. You have a floating mechanism inside the tank, and this thing is connected to a piece of metal that moves back and forth on the pump itself. If you know anything about electricity, this changes the resistance, which therefore gives you a reading on your gas gauge.
Take out the fuel pump and test the resistance. Your multimeter should read 2.4 ohms +or- when full, and around .4 ohms when empty. If you aren't getting any numbers like this, then you need a new sending unit on your fuel pump. Personally, when the gas gauge starts to quit working, its time for a new fuel pump because it's usually not that long after the pump quits working. Fuel pumps are usually good for 120k or 90k miles.Whenever I fill up my car, the gas gauge will say it is half full?Sensor in the tank, it consists of a float (which floats to the top of whatever level of gas you have in the tank) which then rubs against a series of resistances which send a signal to your dash of how much gas is in the tank. If might just be that the contacts on the sensor need to be cleaned, if needed to be replaced it should'nt cost too much. They range from $25 to $200. Cost of labor would be pretty high, as dropping the gas tank is a pain
