My Gas Gauge Reads Empty When It Is Full Of Fuel

One thing I see and hear quite a bit of from customers is that they complain that their fuel gauge is inaccurate or acts very erratically. I’ve been dealing with these type of problems since I got into the business almost two decades ago. The one common factor in most of these complaints is the fuel level sensor.

Late model fuel injected cars and trucks all have their fuel pumps located in the gas tank. There is also a fuel level sensor, or you may know it better as a ‘sender’. It holds the float assembly along with a resistor board that has small little metal ‘fingers’ that touch the board and send the signal to the fuel gauge to display the proper amount of fuel in the tank. What happens when the fuel gauge becomes erratic is that the little metal ‘fingers’ start to deteriorate from fuel additives, corrosion and just plain bad gas.

Now, once there is any type of gap from a small amount of corrosion, these fingers start to touch the resistor board less and less which will send the wrong signal to the fuel gauge. Once this starts to get worse, there will be portions of the fingers that are barely touching and others that are kind of flopping on and off the board. This will send the crazy signal to the fuel gauge. This would be the time you see the gauge going from full to empty on it’s own, or usually after you fill up your vehicle it will act up from the sloshing around of the gasoline.

This can get quite annoying, and will leave you not knowing how much fuel you actually have. These are the times people run out gas because the gauge showed more fuel than they had. Usually now is when they bring it in to the shop!

I’ve replaced hundreds of these fuel level sensors, and every time I take one off I inspect the float arm and resistor board and metal fingers. Every single time, I can physically see the deterioration of the metal. Customers are especially happy to see this so they know what was causing their problem. Repairs like this aren’t usually cheap. Fuel level sensors on newer cars are usually 100 – 200 dollars just for the part, plus usually two to three hours labor depending on the vehicle, sometimes more.

Getting this diagnosed is fairly easy. Just about every mechanic has seen this type of problem. Late model GM vehicles will usually set a trouble code for the fuel level sensor when there is a problem with it. If your car has a code for this, you definitely need a new sensor.

The only bad thing is, there is really no way to completely stop this from happening. Running a good quality gasoline definitely helps and prolongs the life of fuel system components. Just keep in mind when you see your fuel gauge acting funny, get it checked out! You don’t want to be left on the side of the road, alone, and out of gas!

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I’m looking for the location of a sensor on or near the gas tank. Fuel pressure sensor? It is a 2001 Pontiac Grand Prix.

ProTech:
Do you mean the fuel tank pressure sensor?

Unsure, but it sounds like it. Yes

I’m guessing you have a check engine light with a code related to the sensor?

Yes but i do not have that info with me.my ex says basically its the gas cap but that has been replaced.

OK. The fuel tank pressure sensor is located on top of the fuel pump assembly, on top of the gas tank. But without knowing the code, i would not just go and have that replaced. There are codes related the the system that can be another parts problem. Most of the time when people think a bad or loose gas cap has caused the engine light, the problem is usually what is called the “EVAP system Vent valve”.

He says that it might be a sensor. Where would i find this EVAP system vent valve?

That is located inside the drivers side rear wheel well. Again, the code number is the key to deciding what part has failed.

I will ask for the code and get back to you or some one else. thank you for your time. and know how.

Your welcome.