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2G Incorrect Fuel Level Reading

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spyderdrifter

10+ Year Contributor
5,267
711
Jul 11, 2009
Somewhere in, Colorado
I've had this problem just like so many others over the years and with most of the DSMs I've owned. However, it's usually a level sender issue, and now I'm not sure what part is the problem. Normally, my low lever light comes on when there's 1/4 left in the tank, according to the gauge and I've reached 200ish miles since filling it. Yesterday, the light came on at half a tank and the same miles. I've finally had enough and I opened the driver side of the tank up. I wanted to get both sides opened, but only had my multitool, so couldn't open the pump side. So on the driver side, I have like half a tank left...

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Yet the gauge and light show this....

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I watched the gauge when I unplugged the sender, and it dropped to empty like it should. When I plugged it back in, and raised to float to the highest point, the gauge returned to half, and the light came back on. This weekend I'm pulling the pump side out and checking it too, but what else can I inspect? Is there a way to check the light circuit? I know I can check the gauge, but gotta find the info again. Any info is welcomed and appreciated.
 
If you get access to a factory manual on the web, you can do a test to check the continuity of both senders. By raising the float to the top, and bottom, and see what your readings are. The ground for both senders are under the drivers seat. You can check the continuity there as well, From the connecters that plug into the senders on car side. I think there is another test? I’m at work typing this on my phone. No access to that stuff. I remembered what I can at this time. Good luck.
 
I pulled both my level senders out today and measured the ohms on each. I found this while searching for the specs:

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And these are the readings from my senders:

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I remember years ago reading about the GSX senders being split for the empty ohm reading so they're supposed to be in the 50-60 ohm range? Is that accurate? If so, my senders are fine, right?
 
So in your first link, at the end, you mention the 2 wires for the low level light. This is where I think my problem is located. Is there a way I can test these 2 wires to see if they make the light come on, or see that they're causing the light to come on too early? While testing my senders, I did see that the tank was damn near empty and the gauge reflected the level. At this point, I really think my gauge is indeed accurate, and my level light isn't.
 
If you ground the driver side yellow-blue {pin 3} (with key on), the low level light should go on. Note: All of the following tests must be done with the fuel sensors immersed in enough fuel in the tank (> 1/4 full). Then ground the driver side yellow-black {on pin 4, not the yellow-black on pin 1}. If the low level light does not come on you have a problem with the fuel level switch [this is a different sensor than the fuel gauge sender which operates the dash fuel gauge]. Then ground the passenger side yellow-black {pin 3, not the yellow-black on pin 5}. If the low level light does not come on you have a problem with the yellow-black between driver and passenger side. Then ground the passenger side black {pin 6} when the tank is near empty (or thermistor not in the fuel). If the low level light does not come on you have a problem with the thermistor sensor. If the low level light does come on you have a problem with the ground connection (but the fuel level gauge uses this ground so that connection should be good since you say it works).
 
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Just a little update, I brought my gauge cluster into the shop since all my tools are here, and got the resistance specs from my fuel gauge as outlined in the Electrical FSM:

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So based on the data for my cluster and the OEM Specs, my gauge is bad, even though it seemed to be showing the correct level and the light seemed to be bad. I know the test says remove the power supply screw, and I did at first, but had no reading at all, so I did it with the screw in. I still plan to test the wiring this weekend for the low level light, and grab my spare gauge clusters and run the same test on them to see if I have a good one I can swap in.
 
You are supposed to take out the screw at the power supply. You will then put one of the probes on the circle part, that is gold colored around where the screw sits when installed. I guarantee you will see different numbers, closer to what the specifications the manual tells you. Just try that one more time and report back.
 
Yes tsiawd98 is correct. With the screw there, the power supply circuitry to all other dash instruments will be in parallel with the fuel gauge and so the reading will be less. Removing the screw and touching probe to the foil around the screw which goes only to the fuel gauge is what you want.

OR:

You could simulate the fuel sender. Connect the power supply foil (or even tightened screw should work) to +12v and ground screw to -12V (battery ground). Then connect a variable 0-110 ohm (or even 0 to something less than say 200 ohm) resistor (potentiometer) between the fuel gauge screw and ground screw. Turning the potentiometer should change the fuel gauge needle (0=full, 110 ohm (or more) = empty). If you don't have a potenteniometer you can try different resistors between 0-110 ohms one at a time (or even in parallel with each other) to see needle position. Note that the gauge reacts slowly however so it may take 20-30 seconds to react.
 
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I tested my gauge again last night and got some different readings, but not in a good way, maybe..

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Judging by your pics you're still not testing these right. You need to probe the screw THREADS, not the PCB. You're just ohming the entire circuit still. It sounds like your GAUGE is working properly from previous posts though.
 
That's what I was thinking, but went ahead and tested as instructed to get it done. I'll see if I can dig up a screw long enough to reach the threads and not touch the foil though and give that a go as well.
 
Can't you stick the probe tips in far enough without the screws in place? I assume the gauge is what the screw goes into which is what you want to test - not the board circuitry which goes to other things too.
 
That's what I thought too when I first read the test steps. Sadly, my probe doesn't reach the threads in the gauge unit, so I have to find something that will reach far enough.

As you guys have mentioned, and I've thought, I do believe the gauge is actually functioning properly, and I thinks that's evident with the 3rd test location reading in the normal range after the screw had been removed. I know that doesn't automatically mean it's good, but the other two locations changed drastically after pulling the screw, but just tested the wrong spot. I'll update again once I get the probe reading the right spot.

Thanks to all of you.
 
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