Stuck fuel gauge

The fuel gauge in my 1999 Corolla is stuck on Full. My mechanic says it’s the fuel sending unit and will cost $250 to replace. But today, the low fuel warning light came on and it appears to be functioning properly. Does the warning light use a different sensor or does that mean the fuel sending unit is working and the gauge problem is elsewhere? Thanks.

i had that same problem.i would take it to someone esle and see what thay say.but i thank you need a new one or there can be a short some where.

I ask how much diagnosis did the mechanic do to come to his conclusion. Did he make the call on the sending unit based simply on what he has seen before or did he pull the sender and test it? I know my answer already, he made his diagnosis based on a “gut feeling”. Take a look at the area above your fuel tank (under the carpet) and look for a panel to access your sending unit. I have never put a sending unit in this car so I don’t know if dropping the tank is really required.

Spoke to the mechanic this morning. He said they tested the gauge by mimicking the signal near, but not exactly at the sending unit (didn’t catch exactly where that was done) and the gauge worked. Didn’t sound like they tested the sending unit itself.

Do the fuel gauge and the low fuel warning light both work off the signal/wiring from the sending unit?

The block diagram of your fuel sending unit does indicate two resistive circuits (one variable,one fixed) What I conclude from this is that it is possible for the circuit that turns on the light to function correctly but for the circuit that provides a resistance for the gague to be inoperative. My error could be that I am reading too much into a block diagram.

That’s good enough for me. If there are two circuits, that’s a logical explanation for the behavior I’ve seen. Makes sense that the variable circuit would drive the variable position of the gauge and the fixed circuit would drive the on/off warning light. And good to know that I still have some warning even without the gauge. Thanks for the help.