Isuzu Repair: check engine light, negative battery cable, gas gauge

Question
Hi Daniel, I am sure you get this question a lot.  I have a 1999 Isuzu Amigo.  Over the past few years the check engine light comes on after I get gas.  I have been told by a mechanic that it is because the gas cap was screwed on wrong and just take it off and put it back on and drive around.  The light always goes off.  This time I got gas same thing...light came on.  I took of gas cap put it back.  The light went out. Then 2 days later the light came on again but I haven't gotten anymore gas.  I am now concerned that it might be something more serious.  I removed gas cap but light still won't go off. I also have a problem with the gas gauge..it is fine when it is full by then it drops to empty after a few days and my gas mileage is getting bad.  Is this all connected? or am I in for some bad news?

Answer
Well kind of Deborah. The fuel level sending unit is the culprit. 100% positive. It is under 40.00 dollars on ebay and can be installed in an afternoon. The gas tank must be dropped as the fuel pump is inside the tank. Also be very very sure you connect the fuel level sending unit very very gently and do not bend the wire. Also make sure all the connections are good and tight and that the tank o-ring is sealed and that it is pressurized. Before any of this though remove the negative battery cable and that will clear the fault code as well. After the tank has been reinstalled and the battery cable hooked up the fault code will be gone and the fuel gauge will work perfectly. If you have any questions do not hesitate to ask okay??