The fuel level gauge in my 99 Civic is stuck in the full position, most of the time.

Occasionally it would show the correct level briefly and then go back to full.

The gauge is all the way on empty when the car is turned off.

The low fuel light indicator does work.

1. What are some ways to test what is actually not working?

2. What can explain the fact that it sometimes shows the correct level?

Thank you.

 

Sending unit in tank is probably bad (or you have a hole in the float) or a bad wire to the cluster, ground issue.

 

Does the fact that it sometimes shows the correct level but is otherwise stuck on full suggest that it could be a wiring issue / short?

How does the wire travel from under the back seat to the cluster?

 

And what are ways to start testing this?

Thank you.

 

Your probably going to have to pull the tank and measure the ohm values of the sending unit both full and empty (by moving the float arm and reading the output). If that checks out I would read the ohm values of the sending unit line to the gauge cluster. You could always use a potentiometer 0-5 ohm, hook it inline off the sending unit line and see if the gauge moves as it should... if the sending unit checks out its more than likely your gauge...

 

Sounds to me like the sending unit in the tank is bad... but you need to test them...

 

I had the same issue. After testing and verfying that it was not the sending unit. I went to my local junk yard and picked up a fuel gauge out of another civic. Same year, engine and tranny. Pulled out my gauge and popped this one in. Has been working flawlessly. And the best part...i paid $1.00 for the gauge.