Gas Gauge & Light...problems - Toyota Nation Forum : Toyota Car and Truck Forums

87_SR5 · 12-19-2004, 12:59 AM

Hello Everyone,
I have an '87 SR5 4x4 w/ a 22RE and 5spd. I am having problems with the gas gauge. Sometimes it will give me a reading and sometimes it won't. For example...I fill up and the gauge will read full...drive it for a while and eventually the gauge won't read anything, even though there is more than a half tank.....then sometimes it will start to read when the tank gets low, but not always. Or sometimes the guage will read 1/4 tank, when the tank is really full. The only way I am sure of how much gas I have is to reset the tripometer each time I fill up.

So my question is: where should I start to solve this problem? Could it be the gauge in the dash? Or the sensor in the tank? I really don't know how the sensor/gauge works...so any information on that will help. I just don't want to start doing something (like tearing into the dash) when that might not even be the solution.

Is this a common problem? My dad had an '85 and it eventually did the same thing. Also, my friends gauge stopped working completely in his toyota.

Another thing. Just a couple days ago a saw a "FUEL" light come on the dash. I didn't even know there was this light. This is the first time I have seen it for the 3 yrs that I have had the truck. The thing is the tank isn't even empty yet. I don't know whats going on, but something isn't right.

Any advice would be greatly appreciated. I am glad I found this Toyota only forum...hopefully I can fix this problem that I have.

Thanks for any help

CraigW · 12-19-2004, 08:02 AM

I would start at the tank first. (may not be easy to access) I would start by removing cleaning and re-seating the connector for the sending unit. Next would be the ground for the sending unit but that could be tricky as well. If you have to drop the tank I would also maybe pull the sending unit up out of the tank and inspect the float and its operation.

87_SR5 · 12-19-2004, 11:34 AM

Thanks for the reply...If the problem is either with the sending unit's connection or the sending unit's ground, would this cause the problem with the low "FUEL" light that comes on at the dash? Is there a seperate sensor for the low fuel light?, or does it work off the sending unit also?

Thanks for the help

CraigW · 12-19-2004, 12:01 PM

I THINK !! It is all done by one 1 sensor. Getting to it will be the real challenge.

87_SR5 · 12-19-2004, 05:58 PM

I took a look at my manual and the wiring diagram. From what I see, it looks like there are two fuel sending units...a variable unit (for the gauge), and a switch sensor (for the low fuel light). Take a look...let me know what you think.

I agree that it will be a challenge getting to the sensor(s?)....I think I have some other stuff that needs to be done to my truck before I start messing with this. Got my front main seal changed today so that's one thing crossed off my list.

Thanks for the help

CraigW · 12-19-2004, 06:47 PM

You are 100% correct guess I should just SHUT UP

Try to look for a bad ground ?? That would be common to both.

87_SR5 · 12-19-2004, 08:37 PM

I wasn't telling you to shut up...I just wanted to make sure I was reading the wiring diagram correctly. That does make sense to check the ground...because they both use the same ground wire.

I wonder how this setup works with the low fuel sensor. Maybe the float triggers the sensor when it gets down lower...

I don't know.

I will check the ground for sure...I have other electrical stuff to work on also. The owner before had a big stereo system with amp and subs so who knows how much the wiring is messed up.

Thanks for the help

CraigW · 12-20-2004, 05:45 AM

The low fuel light appears to be a switch and fixed resistor, And would only trigger at the tanks lowest level. More than likely they wont do the grounding at the tank itself. So if you can locate the harness from the tank you may may be able to locate that common ground connection.

87_SR5 · 12-20-2004, 02:53 PM

So there switch and fixed resistor that comes off the sending unit that is in the tank...and when the resistance changes in the line from the tank (when there is low fuel), the resistor switch triggers the low FUEL light. Is that correct?

I am just trying to understand what is happening...maybe that switch w/ fixed resistor is the problem with the fuel light, and it wouldn't have to be mounted at the tank.

I will get under there today and check the ground. It appears, from the diagram, that they are both grounded to the line g. In my book, it says that the ground g is located in left side of instrument panel.

I will check it out. Thanks for the help

CraigW · 12-20-2004, 06:48 PM

The switch and the sending unit could be separate could be one unit ?? Make sure you have a meter and or a 12 volt test lamp before starting. You may be able to provide a ground (as a test) it is also possible that it is a supply voltage problem.

87_SR5 · 12-20-2004, 09:56 PM

Do you know where I can find vehicle specific wiring diagrams? The diagram that I have out of my Haynes manual is for typical late model trucks & 4runners. Not everything is there. It would be nice to have...and it may help me out some more.

Not everything is shown on the diagram I have. I still have to fix the door switch for the interior light, and the wire is there, but it isn't attached to anything. I am going to follow the wire from the other door, but a wiring diagram would be nice. I also have a deck lamp switch on the dash and it isn't working...it could be the wiring or the switch. My diagram doesn't show the deck lamp either.

Thanks for the help.

CraigW · 12-21-2004, 05:51 AM

Check with your library and see if they have access to Alldata or ARRC websites. They have most wiring info in PDF format and it can be printed out.

The library may also have your manual.

If you cant find the info send me a PM and I will try to get it for you. Might take a couple of days though.