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Hello new here and need some help. So my gas gauge is faulty and runs out on 3/4 tank...dropped tank and installed new sending unit and didn’t fix the problem. So I checked sending unit/power and ground from tank to cluster and everything is within spec...I couldn’t find any info on checking the gauge cluster is self so I bought a new stepper motor for the fuel gauge and install that today.When I turn the ignition on gauge went to the exact same spot slightly above 3/4 mark(only 5 gal in tank)... I am beyond frustrated and could use any recommendations on what this issue may be. The only thing I can think of to replace next is the whole gauge cluster is self , I inspected the whole circuit board with a magnifying glass in there is no burnt or discolored or cracked solder areas
 

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Mambeau / Admin
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I'm not sure I'm clear on what's happening ...

If you fill up, does the gauge needle go all the way to the 'max' / 'full' position?

My first interpretation is that the gauge can accurately read all the way to max / full if the tank's at least 3/4 full, but the gauge needle stalls out at the 3/4 position and stays there once the fuel load gets down to 3/4 tank or lower.

Have I got that right? Or ... ???
 

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Discussion Starter #3
So if I fill the tank it will go all the way to full. But I run out at 3/4 of a tank. Sorry I should’ve specified better. So the only range that my gauge has is three-quarter to full... but it’s weird because when I turn the ignition off the gauge has full range and will drop down to empty like a normal vehicle So it’s not sticking
 

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Discussion Starter #4
3/4 =empty and full=full.....and it moves super super slow from full to 3/4 which is about 400miles...I’m so stinking confused ha ha Ha
 

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Mambeau / Admin
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OK - thanks for the clarification. I'm glad I asked, because your description rules out what I thought could have been the problem.

Just for the record, I recommend you do the following test (see attached excerpt from the FSM).

The F19 connector is the one back in the rear at the fuel level sender.

I doubt this will be a decisive test, but I want to rule out any weirdness back in area of the sender and fuel tank.

 

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Mambeau / Admin
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Moving on (as I expect will be necessary ... ) ...

As far as I know, the fuel gauge reading is based on resistance (ohms) on the signal line.

If the gauge reads 3/4 when the fuel sender is signaling 'empty', I suspect you have a wiring fault (bad connection; maybe a short) that's affecting the resistance being interpreted at the cluster end of the circuit.

Here (attached) is the 2006 combination meter (cluster) wiring diagram.

Check page 263, where the connections out to the fuel pump / gauge sender are shown.

There are two wires involved, and they both pass through the ID2 connector in your left kick panel.

Pull the kick panel, locate the ID2 connector (look for the orange and yellow/black wires shown in the diagram), check for damage, and make sure the connections are clean and tight.
 

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Discussion Starter #7
Thank you very much so I did that first test at the fuel sending unit plug and everything checked out. So I plug my fuel sending unit back in and turn my ignition key to the on position and I can slowly raise the fuel sending unit and it will stay on empty on the gauge cluster until I hit the three-quarter mark manipulating the sending unit and then it will start registering on up.... if I drop the fuel sending unit arm back down it will do the same thing it’s currently doing and just show 3/4 of a tank but is actually empty position. Where would I find the page listing that you posted for checking that plug? You have no idea this is the best information I’ve got yet thank you
 

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Discussion Starter #8
So I’m going to test the wires between the cluster plug and the kick panel plug and see if it’s inbetween there... I have a massive wiring up there from whoever had the truck before me and put in an auto start antitheft set up
 

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Discussion Starter #9
So checked orange at cluster plug to orange at kick panel and it checks out(0ohm) and yellow/black at cluster to kick panel and 0 ohm as well...so 100% I now know wiring from sender to cluster is ok
 

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Discussion Starter #10
Thank you for all of your help I think I’m going to admit defeat Ha ha ha. I found another post on here from a couple years ago of a guy experiencing the same exact thing the only difference was his ran out on half a tank. It’s pretty much the identical problem that I am dealing with. Sounds like since I’ve already replaced the stepper motor on the back of the fuel gauge that it’s probably something on the circuit bored on the cluster. 400$ here we come:-(
 

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Mambeau / Admin
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... Where would I find the page listing that you posted for checking that plug? ...
Page ME-24 (ME = the Meter section) in the 2005 Tacoma FSM. If there's no Meter section listed in the Table of Contents, look under Body Electrical.
 

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Discussion Starter #12
Yeah I ended up finding all that info. Thank you so much for all your help I have been posting on tons of different forums for weeks and no one gave me even close to the information that you have. I greatly appreciated it now puts my mind to ease that it’s not a wiring issue.On that other guy’s post he was talking about getting 12 V to the circuitboard but it only needs like 5.6 and I have no idea how to check that. I think at this point as circuitboard will be in order
 

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Mambeau / Admin
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If the needle never sank below the 3/4 mark I'd wonder if it was binding inside its housing or interfering with the cluster's face / cover. This has been a common glitch when adding a custom face plate or cover onto a Taco cluster.

The 'logic' inside the cluster isn't explained anywhere in the factory documentation, so the 2005+ cluster's inner workings are even more mysterious than they were for the 1995.5 - 2004 generation.

If you look at the wiring diagram you'll see that the fuel sender connections link to something called the 'Fuel Control Unit' inside the cluster. My guess is that this is a chip or maybe a particular circuit within the circuit board, and that it's somehow gone bad.

I have no idea whether this Fuel Control Unit is a separate component that can be swapped out.

If you're confident you've ruled out wiring issues from the cluster back to the fuel sender, I suppose there's no choice but to have the cluster itself (the circuit board) checked out.

One other random thought ....

Is it possible the fuel tank float (whatever) is hanging up and unable to drop below the position that gets interpreted as 3/4 of a tank?

I'm asking because you only mentioned replacing the sending unit itself, and didn't mention anything about checking any mechanical components used to measure fuel level.
 

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Mambeau / Admin
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Something I should have thought to ask earlier ...

Have you actually run out of gas since this weird behavior started?

If so - or when you were testing the sender position (arm) against the gauge readings - did the low fuel warning light ever come on?

If the fuel level (or arm position) was ever in the critically empty range and the light didn't come on, I'd tend to think that suggests the Fuel Control Unit in the cluster is screwy.

Unfortunately, there's another possibility ...

It's conceivable something about the float / arm / sender apparatus is interfering with the variable resistor's ability to generate a resistance / signal at anything less than "3/4 fuel level."
 

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Discussion Starter #15
There’s no obstructions in the tank with the lift and lower arm because I had the whole assembly pulled out when I was manipulating it.
To answer your next question yes I have run out of gas multiple times ha ha and it’s always in stop and go traffic and it always runs out with 3/4 of a tank on the gauge and now the fuel light does not come on.
The only way I have been able to get the low fuel light to come on and read Empty is if I unplug the sending unit/or during testing procedure if I recall....
 

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Discussion Starter #16
Forgot to mention that the low fuel light will never come on at all unless you unplug the sending unit itself from the gas tank
 

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Mambeau / Admin
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So I’m going to test the wires between the cluster plug and the kick panel plug and see if it’s inbetween there... I have a massive wiring up there from whoever had the truck before me and put in an auto start antitheft set up
This bit about the auto start / antitheft rig bothers me.

Antitheft devices commonly get wired into the fuel pump (or associated) circuits, because killing the fuel supply is one of the most secure ways to keep the vehicle from running.
 

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Mambeau / Admin
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Forgot to mention that the low fuel light will never come on at all unless you unplug the sending unit itself from the gas tank
This is almost certainly a critical clue, but I suspect it doesn't point to one and only one possible fault.

The fuel warning light is at the 'tail end' of the circuit, and whether or not it lights up depends on both the sender unit and the Fuel Control Unit in the cluster (not to mention the wiring).

Unplugging the sender unit kills the signal (resistance reading) on the line from the sender to the cluster. As such, it obviously suggests the sender unit is sending a bad signal (never lower than 3/4 level). However ...

It just as easily suggests the sender end is fine but the Fuel Control Unit isn't functioning correctly (i.e., never triggering the warning light).
 

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Discussion Starter #19
Yeah so I don’t know if it’s hand-in-hand or what but there was a little black box up under the dash that said valet
 

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Discussion Starter #20
So I could even possibly have a wire hooked in somewhere that when I turn my ignition key on it could supply power into the fuel sending unit circuit? Do I understand that correctly I’m horrible with power as you can tell
 
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