Fuel Sending unit testing...conflicting info??

[Full_Throttle]

Hi gang,

I have been troubleshooting a gas gauge problem, and in my research I have come across what appears to me to be conflicting information.
Several people have cited this website for troubleshooting the fuel gauge system. One of the links at this site has the following information for a 1999 4runner;

"INSPECT FUEL SENDER GAUGE
Measure the voltage between terminals 2 and 3 for each float position.
If resistance value is not as specified, replace the sender gauge."

Even though it says to measure the voltage, I am sure it means resistance. So, according to this page, the resistance should be between 4.6 ohms and 0.3 ohms depending on the amount in the tank.

NOW, compare that to to what I have found on 1996 to 2002 Toyota 4Runner OEM Repair and Wiring Manuals specifically HERE

The important stuff is on pages BE-51 and BE-52

Note how to test the resistance of the sending unit, and how to check the gauge.

INSPECT FUEL SENDER GAUGE
Measure the resistance between terminals 1 and 3 in each float
position.
Float position: mm (in.) Resistance (Ω)
F: Approx. 39.4 (1.551) Approx. 184Ω
1/2: Approx. 56.0 (2.205) Approx. 97Ω
E: Approx. 148.9 (5.862) Approx. 12Ω

What is different between these two sources is the pins used to measure and the resistance measured. Can anyone confirm which way is correct?? When I measure using pins 1 and 3, my resistance measurements are in line with the chart, but when I use pins 2 and 3, they are way off....

I am not sure what to think here. I tend to believe the 2nd one since it appears to be from the FSM, but the first one looks legit as well??

Can anyone with a known working system take the time to take these measurements and confirm which set of instructions are correct?

 

[Stick Figure]

I would guess "Lars" had a typo. I would also say your problem is probably with the cluster, but you haven't given enough info to confirm that. Find the full wiring schematic and see where those three wires go, you should be able to confirm at the vehicle then which of the terminals is the proper way to measure things.

 

[Full_Throttle]

Hi,
I understand how to troubleshoot the system, my problem is which figures and pins do I use? Do I go with pins 2 and 3 and resistance figures below 5 ohms OR do I go with pins 1 and 3 and figures in the 180 ohm range (assuming full)?

I have pulled the cluster and performed measurements and checked the vin # against the TSB and I already have the upgraded circuit board. It would be nice to be able to confirm through measurements that the sending unit is faulty.

My problem started after I ran a wire through the firewall rubber boot in preparation to adding aftermarket lighting. I didn't splice any wires or anything like that, I used a fuse tap to connect to a switch to then activate a relay under the hood. All I did was to RUN the wires, the aren't connected to anything. The next morning my gauge read full even though I had less than full in the tank. After I got to my destination, the next time I started the vehicle the gauge dropped to empty and the fuel light started flashing. I have checked the measurements on the back of the gauge, and they are close to 160 ohms like the manual says. I just want to determine if the sending unit is the problem or not....

 

[ChildrenOfBodom]

1999 Limited?

Why not just replace the fuel sending unit as well as just the cluster motherboard as indicated by Toyota TSB?

1999 Toyota Truck 4 Runner SR5 4WD V6-3378cc 3.4L DOHC (5VZ-FE) MFI - Instruments - Fuel Gauge Inaccurate

It worked on my 99. I had the exact same problem. Don't waste your time with the old sender, all 99-00 fuel sender units within the correct vin ranges are technically bad... hence why they made a new version for the TSB...

Save yourself this huge headache...

Fuel sender unit and gauge cluster motherboard

 

[Full_Throttle]

I agree that my issue with the 4-runner is probably the sending unit.

Anyone have an opinion as to the proper ohm readings and the pin outs?

 

[carkivey3]

going thru same thing

over a year since your post but i would like to know the outcome as i am troubleshooting one now

 

[EatonKyleH]

over a year since your post but i would like to know the outcome as i am troubleshooting one now

Perhaps this may help you.


1. Perform the calibration procedure as per TSB #EL010-99. This needs to be done if the fuel gauge is replaced.

2. At the fuel gauge sending unit, check for 5 volts at the Yellow/Red wire and for ground at the Brown/Black wire.

3. Disconnect the fuel gauge sending unit and connect terminal 2, Yellow/Red wire to terminal 3, Brown/Black wire through a test light and verify that the gauge moves towards full. If it does, test the resistance of the fuel gauge sending unit to be about 184 ohms at full, about 97 ohms at half, and about 12 ohms at empty.

I assume you are already familiar with this TSB for your 99? If not I've thrown it up here too.

 

[So Many Roads]

[MENTION=50784]Full_Throttle[/MENTION]

Did you ever solve the fuel gauge problem? I read through your build thread but didn't see a resolution. Just like you did, I wired up a relay (for a horn) and then started to have the fuel gauge issues (fuel gauge reads 100% full, or 100% empty with blinking fuel light).

Hoping you were able to resolve and might be able to point me in the right direction.

From other threads it looks like a faulty ground can cause this problem; I spent the afternoon checking grounds for continuity but didn't find any issues.

Thanks,
SMR