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I tried searching for this, but to no avail.


I have a 60 gallon RDS fuel tank/tool box combo that I'd like to install in the bed and plumb into my fuel tank. I had heard that this could cause codes on the dual-tanked trucks due to the computer seeing fuel flowing into one tank but not leaving another.



I have a single tank setup on a 2019 3500, and according to the local dealer, this shouldn't cause a problem, but he was not 100% as they hadn't seen it yet.



Anyone out there have a tank rigged up to a new L5P, and how'd you plumb it in? Thanks!
 

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Thread relocated over to "Fuel System, Air, Exhaust, & Emissions Upgrades"
for better responses

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I have a 45 gallon aux. tank and solenoid valve on mine and flip the switch inside when I need it and turn it off when I'm full. On my 2003 I just had a manual valve and left it open all the time and after driving ~150 miles my fuel gauge would show empty but once the aux. tank ran empty and my main tank level started dropping the fuel gauge would start showing a level again.
 

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Same basic setup, no issues on an 2019.
 

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I've got an RDS 40 gal. tank w/toolbox combo in my 2018 3500 DRW. Originally it was plumbed as a gravity feed into the OEM fuel inlet hose to the OEM tank. I'm still using the same plumbing, but put in an inline fuel pump instead of using a solenoid valve for gravity feed.

I've had this setup for several months with no problems or codes/messages.
 

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I don't have an aux tank, but I'm been on this forum for over 14 years . . .

Discussions on this topic, even years ago, suggested that GM put "sanity" checks in the some of computer programming. So, if you're driving along and the fuel tank is getting fuller . . . insanity!! . . . so it knows something is wrong. To be safe, it would set the fuel gauge to E since it lost confidence in the sensor reporting.

The easy solution is to only transfer fuel when parked (rest area, lunch, etc., when traveling). Or if done while moving, accept that it might complain and set codes and point to E; then just reset (if codes) at some convenient time later, and I would expect the fuel gauge would come back to life, too.
 

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Discussion Starter #7
Appreciate the replies!



I had one on my old '07 Dmax, with a pump, without any issues at all. I even plumbed it in through the vent tube instead of the actual filler neck. I just wanted to make sure everything was still legit.


jake111: I never got any "insanity" codes or anything running down the road while filling. That's what I was hoping not to happen with the new trucks either. Looks like the other guys are doing fine with it. I'll keep my fingers crossed. Looks like cwq21 was having this "sanity" issue on his '03.
 

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Appreciate the replies!



I had one on my old '07 Dmax, with a pump, without any issues at all. I even plumbed it in through the vent tube instead of the actual filler neck. I just wanted to make sure everything was still legit.
This IMO this is the better way to plumb thru the vent tube with a T.
Slower transfer, less chance of issues with the fuel gauge.
Just remember to pay attention to the fuel gauge as your transferring, when it hits about 3/4 tank stop the transferring.
It’ll continue to go up a little from there.

I have a RDS 60 gallon aux tank with tool box, electric pump with normally closed solenoid on a switch when running warning light in the cab, powered only when ignition is on.
I recently added a 3mm amber LED flashing light next to my CTS2 on the dash, much easier to see when fuel is transferring, so hopefully I won’t forget.
 

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FYI, the idea of having a electric pump and a normally closed solenoid wired inline ign powered is double protection if one was to fail allowing fuel to flow.
This is how most of the shops that’s license to install auxtanks.
 

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It isn't the gauge going up that's an issue, it's the gauge not going down as expected. This is most common on larger replacement tank installed in the stock tank location.
 

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I have a NC solenoid wired through the ignition and it's gravity fed.
When traveling, I turn the switch on when the fuel level is at about 1/2 tank and turn it off when full. No issues with the computer thinking the gauge is faulty.
 

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I have a 45 gallon aux. tank and solenoid valve on mine and flip the switch inside when I need it and turn it off when I'm full. On my 2003 I just had a manual valve and left it open all the time and after driving ~150 miles my fuel gauge would show empty but once the aux. tank ran empty and my main tank level started dropping the fuel gauge would start showing a level again.
I'm in the process of an identical install on my 2018 3500HD Duramax. As I tee'd into the filler neck it occurred to me that pumping fuel while driving (factory fuel cap on, of course) would (might?) cause positive pressure in the filler neck and tank. Did you do anything vent the positive pressure? Any issues as a result of the positive pressure? Thanks for the help.
 

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Less problems when you T into the vent line and stop transferring when your gauge gets to about 3/4.
The gauge is slow reacting to the fueling, if you allow it to get to full I think this is one reason some have gauge issues and not corrected until you shut down and restart.
I’ll stop mine at 3/4 by the time the gauge settles mines close to full.
 

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I have a RDS 60 gallon aux tank with tool box, electric pump with normally closed solenoid on a switch when running warning light in the cab, powered only when ignition is on.

I also have an RDS 60 gallon aux and with tool box. I had an electric pump failed after nine months of use (twice) I decided to go to gravity feed. Now I'm getting the P0461 Fuel Level Sensor A circuit Range /Performance fault (fuel gauge reads empty and check engine light). I need to go back to the pump.

What electric pump and solenoid valve are you using? Thanks.
 

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I use a Facet pump w/no solenoid. The pump is designed to internally prevent thru-flow unless the pump is running. Never had an issue with the tank draining thru the pump when the pump is off. I have a manual fuel shutoff at the tank outlet located in the bed of the truck. I'll keep this closed off unless I intend to use the aux tank which I only do when towing my RV, but even with it open the tank will not drain unless the pump is on.
Facet makes lots of different pumps for pretty much any type of service. If you want a pump that does allow flow-thru they have them. My pump is one of their 'Gold Flo' models. A small cylinder designed to be mounted vertically & has an inlet and outlet port. Also has a built in strainer that's removable for cleaning/replacing.

Facet's website has features to help you sort thru all their pump types/purposes.
 

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There’s many that will work
Normally closed solenoid
Fuel Tank Selector Valve - Universal CRB22057
Mines from NAPA

Fuel pump
Carter P4070 In-Line Electric Fuel Pump
Amazon carries this

The solenoid is used as a safety back up incase fuel gets by the fuel pump, wired inline with the fuel pump on ignition power with a switch in the cab.
Aux tank fuel pulled thru the top thru fuel filter - fuel pump - solenoid - to main tank T into the vent line.
Picture sideways, but this should give you a idea.

I’ll pm you the links
The links will not work, sorry
 

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I use a 3/8” ball check valve, available at any marine supply shop. I too have plumbed mine into the relief vent hose, near the filler cap. You also might consider a return line, since your auxiliary tank is bigger than your main tank, so if you forget to turn off the pump you won’t have a Exxon Valdeze-sized spill to deal with.
 

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My auxiliary tank is plumbed into the filler hose. I fill up the main tank first, then fill up the bed tank. I leave the valve open all the time. My gauge reads full until the bed tank is empty and then the gauge acts normally. If I drive more than 150 -200 kms. at a time, the gauge will drop to empty and check engine light comes on. BUT, it automatically resets when you shut truck off. Had it in my '11 for 8 years and my '15 for over a year, ZERO troubles, no leaks, Nada!( just don't take factory filler cap off when bed tank is full!)
 

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Me having my AirDog return line plumbed into the fill neck, the vent was the best option.

It’s not easy to control a ball valve from inside the cab if ever needed, you’ll have to pull over and get out.

Having a solenoid valve would be a better option to open and close when needed from inside the cab.
Gravity flow and having gauge issues and codes try just cracking the valve open for a slower fill.

Checking your state dot laws on plumbing a aux tank might be worth doing, if your ever in a accident and a fuel spill is present there will be a very large fine, no questions asked.

I have this switch with light when my transfer pump is on, I also have a small flashing LED light next to my CTS2 as a constant reminder when fuel is transferring .
 

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Ball CHECK valve. It is a spring-loaded ball that automatically opens when the pump is running, but closes when the pump is off, preventing siphoning.
 
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