My gas gauge tends to swing wildly

August 1, 2013 | By Jim Richardson


I am having gas gauge issues regarding my 2000 Blazer. The dash gauge appears to read correctly until the tank’s level reaches a half-full condition. From that point on, as the tank volume depletes, the gauge swings quite wildly, indicating a level at any point somewhere between empty and full. Then, if the tank gets very low, the gauge needle steadies at “E” and the “Low Fuel” warning light does come on.

Another curious trait is that, for the most part, at any point in the tank’s fuel level, if I put the automatic transmission in neutral—say at a stoplight—the gauge will exhibit the wild swings between “E” and “F” as it does when the tank’s below half-full.

I was wondering if you or the readership could hazard an opinion, given the provided evidence, if the source of the trouble might lie with the gauge or the sending unit.


The symptoms indicate that your problem is the gas gauge sending unit. Unfortunately it is in the fuel tank, which you will have to drop to gain access. Run the tank almost to empty before dropping it, and needless to say, don’t smoke while you are doing this, work outdoors, and keep a fire extinguisher nearby.

Also, you need to know that the sending unit is only available as part of the fuel pump module (approximately $85).

Of course, you’ll benefit from the new pump, so that should be the last time you have to drop the tank. A new O-ring usually comes with the sending unit/ fuel-pump assembly, so make sure it is included. It is also wise to get a new tank-locking ring as well. You won’t want to have to go back to the parts store again if you tear up the old one.

Finally, the module must be properly grounded to work. I like to run a special ground wire from the module to bright clean metal on the frame or sub-frame of the car to make sure.