1999 Le Fuel Gage Permanently Full - Toyota Corolla, Chevy Prizm (1998-2008)

Here's the deal - With gas prices as high as they are these days, have you ever dreamed of a gas tank that never empties? Well, I have one (sort of).....

My 1999 LE gas gage is stuck on full. It won't budge. I almost ran out of gas, not paying attention, until the low fuel indicator light came on. I thought "how can I almost be out of gas, when the gage reads full?"

I did some reading - some say it's the gage itself - something about variable resistance - the emptier the tank gets, the lower the resistance, and the lower the gage needle reads. Conversely, the fuller the tank, the higher the resistance, the higher the needle reads. I have no idea how to measure the resistance going to the gage from the sending unit.

Others say it's the sending unit, which is attached to the fuel pump, located inside the gas tank, under the back seat.

Well, I took out the back seat, located the access panel for the fuel pump. There's wires. No obvious signs like loose wires, corrosion, etc.

Now what? How do I check whether it's the gage, or the sending unit? Each one sells for about $125.00 - I would hate to pick the wrong one, and end up in the hole any deeper.

Any help would be greatly appreciated.

KMC

its probably the guage, the light comes on because the sending unit resistance drops below a certain level.

Bikeman982

It could be the gage - you would have to take off the instrument panel to check it, or it is the sending unit.

I had no reading on my gas guage and I pulled out the whole assembly from under the rear seat.

I replaced the sending unit and now it works perfectly.

It may be the same for you, or maybe a stuck gage.

It could be the gage - you would have to take off the instrument panel to check it, or it is the sending unit.I had no reading on my gas guage and I pulled out the whole assembly from under the rear seat.

I replaced the sending unit and now it works perfectly.
It may be the same for you, or maybe a stuck gage.

How would I "check it out"? I've had the actual gage out of the instrument cluster - I held it in my hand. I have no idea what to look for. I tried moving the needle down (towards "E"), but as soon as I reassembled it, and powered up, it went back to full.

KMC

The steps to check it are quite involved - one quick and simple test to determine if the gauge is at fault or the sending unit from the float is to disconnect the sending unit at the fuel pump (under the rear seat, directly behind the driver's seat). Should be a 5-pin connector. Turn the ignition to ON - the gauge should read E - if not, you got a bad gauge or shorted wire somewhere. If it does show E - then you probably have a bad tank sending unit.

The steps to check it are quite involved - one quick and simple test to determine if the gauge is at fault or the sending unit from the float is to disconnect the sending unit at the fuel pump (under the rear seat, directly behind the driver's seat). Should be a 5-pin connector. Turn the ignition to ON - the gauge should read E - if not, you got a bad gauge or shorted wire somewhere. If it does show E - then you probably have a bad tank sending unit.

Thanks - I will definitely check this out.

KMC

Bikeman982

The gage responds to the imput from the sending unit. It usually only sticks if it is physically jammed, or the spring is either broken or lost it's gradiant (strength). My bet is that the resistance strip on the sending unit is bad - but that's just my guess.

People think that if their gage does not work that the gage is bad, but that is not necessarily true.

The steps to check it are quite involved - one quick and simple test to determine if the gauge is at fault or the sending unit from the float is to disconnect the sending unit at the fuel pump (under the rear seat, directly behind the driver's seat). Should be a 5-pin connector. Turn the ignition to ON - the gauge should read E - if not, you got a bad gauge or shorted wire somewhere. If it does show E - then you probably have a bad tank sending unit.

Well. I did what you said - I unplugged the wiring harness, turned on the ignition, and the gage dropped like Enron stock. I reinstalled the wiring harness, turned on the ignition, and the gas gage went back to full. Sounds like a bad sending unit to me.

Thanks for the help figuring it out.

Now - any tips on replacing the sending unit? I should be able to figure it out, but if there are any words of wisdom, voice of experience etc., I would appreciate them.

KMC

do it on a nearly empty tank, have rags handy, let the pressure out of the fuel tank via the fuel fill cap.

Bikeman982

The steps to check it are quite involved - one quick and simple test to determine if the gauge is at fault or the sending unit from the float is to disconnect the sending unit at the fuel pump (under the rear seat, directly behind the driver's seat). Should be a 5-pin connector. Turn the ignition to ON - the gauge should read E - if not, you got a bad gauge or shorted wire somewhere. If it does show E - then you probably have a bad tank sending unit.
Well. I did what you said - I unplugged the wiring harness, turned on the ignition, and the gage dropped like Enron stock. I reinstalled the wiring harness, turned on the ignition, and the gas gage went back to full. Sounds like a bad sending unit to me.
Thanks for the help figuring it out.
Now - any tips on replacing the sending unit? I should be able to figure it out, but if there are any words of wisdom, voice of experience etc., I would appreciate them.
KMC

Can be done at anytime, but lower fuel level means less gas spillage.

First remove the fuel tank cap (gas cap) to relieve pressure.

Keep a rag under the fuel lines when you disconnect them as some fuel will spill out.

Be careful with the bolts as you don't want to drop them into the tank or stuck between the seat and car frame.

Carefully angle the sending unit out of the opening without damaging the fuel level float located at the bottom of the assembly.

I have changed them on different cars and they are not too difficult to do.

IMPORTANT - Don't smoke when you do it!!

I have sorta the same problem, mine just doesn't stay at full, It just doesn't read correctly sometimes. I figured out my problem, it was the sending unit, but I didn't replace it, I just use my mileage.

I have sorta the same problem, mine just doesn't stay at full, It just doesn't read correctly sometimes. I figured out my problem, it was the sending unit, but I didn't replace it, I just use my mileage.

Yeah, I use the mileage too - I reset the trip meter after each fill up at the gas station......using the mileage and the low fuel light should keep me out of trouble, but it is nice to have a working fuel gage -

I have sorta the same problem, mine just doesn't stay at full, It just doesn't read correctly sometimes. I figured out my problem, it was the sending unit, but I didn't replace it, I just use my mileage.
Yeah, I use the mileage too - I reset the trip meter after each fill up at the gas station......using the mileage and the low fuel light should keep me out of trouble, but it is nice to have a working fuel gage -

yeah, it is, I wish mine worked right too, but I guess you gotta do what cha gotta, do but I hope my info has helped you in some way.

Bikeman982

I have sorta the same problem, mine just doesn't stay at full, It just doesn't read correctly sometimes. I figured out my problem, it was the sending unit, but I didn't replace it, I just use my mileage.
Yeah, I use the mileage too - I reset the trip meter after each fill up at the gas station......using the mileage and the low fuel light should keep me out of trouble, but it is nice to have a working fuel gage -
yeah, it is, I wish mine worked right too, but I guess you gotta do what cha gotta, do but I hope my info has helped you in some way.

When my gas gage read "empty" all the time I just went by my mileage.

I wanted it working so I got a used sending unit from a local junkyard (cheap) and swapped it out.

It is really easy to do.

Now the gas guage works great and I can see it go to "full" after I fill up and then to "empty" as I drive.