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Discussion Starter #1
owners manual says nothing about this system at all. Does it make any difference which tank gets filled first?
From what I have found out, it uses a transfer pump in the rear tank to feed the front tank which feeds the engine. The only quantity sensor is in the front tank and it supposedly uses an algorithm to calculate total quantity.
Anybody have one of these systems on their truck? My previous 4 3500's were all single tank trucks.
Thanks for any guidance
John R Dunn
 

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First I've heard of dual tanks? What's the owner's manual say the total capacity is?

Maybe there are floats in each tank and the transfer pump keeps them even?
 

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Cab & Chassis models have dual tanks standard, 23 gallon front, 40 gallon rear.
 

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Discussion Starter #5
Well, a little info on the dual tank system for anybodys info.

Front tank is 23.5 gals. and the rear is 40. You will find that the fuel quantity gauge reads both tanks by an algorithm. When mine shows 1/8 remaining, I filled the front first and it took 10.7 gals. The rear took 34 gals. The system uses a transfer pump to move the fuel to the front but will stop transferring when it reaches a certain level to not run the tank/lines dry. I don't think it makes a difference which tank you fill first as long as you don't have the truck running and try to fill the rear first-- it will try to transfer fuel to the front if it is low.
Also, the fuel filter is mounted in front of the REAR tank, not the front like a single tank truck.
 

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I have a 2016 Cab Chassis 3500 Crew Cab Duramax with just now 23k for miles.

I just had my first issue with my dual tank set up. I used to fill the front first but it always spit fuel back after 4 or 5 gallons so I just always filled the rear. I filled up yesterday as normal I typically don't shut off the engine when traveling unless I absolutely have. After filling up I drove about 10 miles then the engine threw a code DTC P2636. The check engine light came on, the DTC said low fuel and the gage dropped to Empty.
I called the local dealer as I was out of town traveling home and they were no help, finally called another dealer and he said to just keep the front tank full and I should make it home. So I stopped a couple times and squeezed in some fuel.

Took it to the dealer this morning and I asked about the recall on the fuel transfer that was done in June 18, about 10k miles ago. He said it was done I asked then what went wrong he said it was I did not shut the truck off and fuel the front tank that caused the problem. That does not make any sense to me, what sensor would know that I was fueling other than the gauge, and why would it matter what tank, as I was told that the recall was to by the pump.

Before this truck I had the exact truck except it was a 2006, it was dual tank etc.. I never had any issues with it but a turbo code on a trip to Maine and the dealer replaced it (turbo) around 92K.

Someone enlighten me.
 

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Discussion Starter #7
I think the second dealer didn't know how the system works. If GM didn't change it up I would think it would be like the ones I have. I don't shut down just to fuel and have had zero problems. I will fill the front first then the rear. If the front is low, and you fill the rear, once the transfer pump senses enough fuel it will start to send it to the front tank because it senses front low and will continue to send it until the front is full. On mine, if I had 1/8 showing on gage I filled front first then rear otherwise I just filled the rear.
Don't understand what went wrong with yours unless the transfer system quit or the gage is off. Post up what you figure out please.
 

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Interesting, I’ve found on my 2019 chassis cab that I have to fill the rear first and the front generally doesn’t take as much fuel. I may try to fill the front next time, but generally even near 1/4 tank the front appears to be full.
 

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I just got a 2015 HD3500 cab Chassis and while driving it yesterday with the fuel gage showing a quarter of a tank the low fuel light came one and the gage dropped to empty. Also the check engine light came on. I put fuel in the rear tank and then today put fuel in the front tank but was able to get just a little in. I had the code checked and it was the P2636 code which is the was the transfer pump but it must still be working as the front tank still seemed full. Any ideas would be helpful. thanks, Steve
 

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Discussion Starter #12
Steve,
I was just reading the new GM TECHLINK newsletter. It has an article concerning the 15-19 trucks with dual tanks. Has to do with dirt on top of the rear tank blocking the tank vent fitting. Can make transfer slow etc. Post what you finally find out what is happening.
 

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I am new so please forgive my newbie/ness. I have just purchased a 2017 2500hd duramax. The fuel gauge shows I am 1/2 full. It appears I have two fuel tanks as indicated but two small lights at the bottom of the gauge. One is only 1/8th and the other full. My miles says I can go 541miles. Owners manual says the rear tank empties first and then the front. I have only one fuel cap. I went to the station and after 2$ the handle turned off meaning the front tank is full. This has to be for the front tank. How do I fill the rear tank? I would figure these would have a crossover pipe to even them out and fill both tanks at once or a second fuel cap. Can anyone help me figure this out?
 

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Do you have the owners manual? All dual tank trucks I've seen have 2 filler ports but those were flatbed equipped. The rear will not empty completely or the lines would have air in them. Is your second tank installed behind the diff between the frame rails where the spare normally goes?
if you have only one gauge how do you know how much is in each tank? What do the lights do?
Sorry for all the questions-- all my dual tank trucks were WT's.
 

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I am new so please forgive my newbie/ness. I have just purchased a 2017 2500hd duramax. The fuel gauge shows I am 1/2 full. It appears I have two fuel tanks as indicated but . One is only 1/8th and the other full. My miles says I can go 541miles. Owners manual says the rear tank empties first and then the front. I have only one fuel cap. I went to the station and after 2$ the handle turned off meaning the front tank is full. This has to be for the front tank. How do I fill the rear tank? I would figure these would have a crossover pipe to even them out and fill both tanks at once or a second fuel cap. Can anyone help me figure this out?
Factory didn't put dual tanks in a 2500 or 3500 pickups..
They were only in the chassis cab 3500's. (a 40 gallon and a 23 gallon; they can be ordered with either or both)

If the truck is 'factory' it will have a 35 gallon tank (136L).
541 miles for a full tank is possible.

Seems like maybe the full sender is working so the computer has good info, but the gauge dial is not.

Mine is a daily driver that runs mostly rural 2 lane. Regularly run it 600 miles between fills.

I don't know what you mean about 'two small lights at the bottom of the gauge'.
 
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