My gas gauge used to go to "E" when I turned it off and now it goes to the "half tank" mark. Once I turn it on now it goes past the "F". it is almost like the guage thinks that the tank is "half tank" mark is the "E". How do I get it back to normal, were when I turn it off the dial goes back to "E".

 

Two things could be wrong here.

(1) the tank sending unit could be faulty

or...

(2) The mechanism/motor that operates the dial indicator is bad (mechanism if its an early gen monte, or motor if its a 6th or seventh gen)

In my old 05 ls all of the gauges started reading incorerctly, getting stuck, etc. This is a common problem on all chevy models that were produced in the early to mid 2000's, especially the montes and trailblazers. I sent it off to some guy in iowa through a local shop and had all of the gauges rebuilt for right around 250 dollars. But since its just the one gauge, I would bet your tank sending unit is the culprit.

 

It could be and I know for a fact cause it has happened in my 97. The computer has gone bad. I did all the checks on mine and it came back to the pc. I replaced and works perfect...

 

I don't think this is the fuel sending unit, because the sending unit shouldn't be able to command the needle go past full.

I'm going to say it's a stepper motor failure. Again, like above, that is if it is a current Monte

 

I'm inclined to agree with chibiblacksheep I think its the stepper motor in the cluster for that gauge.

My wife and I own an '05 Trailblazer that has had the speedometer acting haywire. Its the only gauge to not read correctly. So I know that this stepper motor problem can plague just one gauge. In your case I bet its affecting the gas gauge only.

There is a guy on Ebay out of I think Wisconsin or somewhere that will replace all the stepper motors in that cluster for you for like $60 I'm thinking if I remember correctly? If you are handy with soldering you can probably do it yourself. The stepper motors are extremely cheap on Ebay.