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Diagnosing dual tank balance module

It's definately a unique system. Don't know why they couldn't have just stayed with a dual tank switch and selector valve.
 
THEFERMANATOR said:
It's definately a unique system. Don't know why they couldn't have just stayed with a dual tank switch and selector valve.
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I want to thank everyone for their comments; and Matt for starting this conversation years ago. I have a 2000 Chevy Sierra (gas, though, not diesel. I feel so inadequate with you guys!) and was trying to figure why I always pump 6-12 gallons in the front tank, while the rear only takes 8. I guess I should be happy that I don't run out of fuel!

And you'se are right; I also like the Ford system of a manual switch for the tanks.
 
I just noticed that it didn’t post everything that I wrote above. I was going to say hang around because this group talks about a lot more than just diesels.
 
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Matt Bachand said:
Anyone with dual tanks having problems with fuel gauge or the automated balance flow system this may help.

This module is located by the front (main) lift pump. Slightly toward the rear of vehicle along the frame rail.

On top of this module is a fuel pump balance relay, it turns the rear pump on as needed to transfer fuel.

At the module, you have a harness with 6 wires. Unplug it and check the following with a digital volt/ohm meter

Terminal A- Pink wire, should be 12 volts with key in run position. Fuse is in underhood fuse/relay center marked IGN E 10 AMP

Terminal B- Light Blue wire, this is the signal wire from the secondary (rear) fuel tank, using an ohm meter, measure the resistance from a good chassis ground to this wire and should get a reading between 0 and 90 ohms, 0 is empty tank and 90 is full.

Terminal C- Dark Blue with White tracer wire, this is the signal wire from the primary (front) tank, test is same as for terminal B

Terminal D- Light Green wire, this wire controls the Fuel Pump Transfer Relay, with the ENGINE RUNNING and the front lift pump working, GROUND this wire, the Fuel Pump Transfer Relay should click and then you should be able to feel the rear pump working. If the relay clicked and pump is not working, connect a test light across the rear fuel pump harness connector and see if you have power. If lighted, then replace pump, if not lighted replace relay providing you have 12v at Terminal A.

Terminal E- Black with White tracer wire, This is the ground wire for the control module. Using a test light jump from Terminal A to Terminal E with key on, the test light should be lit.
Terminal F- Purple wire, this wire is the output signal to your fuel guage.
Gound this wire it should read empty, leave this wire open, the fuel guage will go pass full.

The fuel pump relay, which is right above the module, has a wiring harness with 4 wires. They are:

Pink Wire is 12 volt from the same source as Terminal A.

Light Green wire (thicker gage) is the feed to the rear fuel pump.

Light Green wire (thin gage) is the control wire from the module as explained in Terminal D.

Gray wire is 12V from the primary pump circuit to energize the Fuel Pump Transfer Relay.
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I have a 2007 6.0 Liter gas with the dual tanks , I'm not getting power to my rear pump, and my gauge is showing empty with a full front tank. And the truck and front pump runs??? checked all the fuses and relays under the hood but cannot find this "module" your talking about?? Any thoughts?
 
Dennis1980 said:
I have a 2007 6.0 Liter gas with the dual tanks , I'm not getting power to my rear pump, and my gauge is showing empty with a full front tank. And the truck and front pump runs??? checked all the fuses and relays under the hood but cannot find this "module" your talking about?? Any thoughts?
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Your truck doesnt have one. The balance tank module was used on the older body styles. Yours is all done through the PCM.
 
THEFERMANATOR said:
Your truck doesnt have one. The balance tank module was used on the older body styles. Yours is all done through the PCM.
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So the primary pump tells the rear pump when to turn on and off? So the primary pump is most likely at fault? I did check the wires between the two pumps and they seem to be ok?
 
Dennis1980 said:
So the primary pump tells the rear pump when to turn on and off? So the primary pump is most likely at fault? I did check the wires between the two pumps and they seem to be ok?
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No, the PCM controls it all on yours. If any fault is detected in either sender or the rear pump doesn't transfer fuel, the PCM defaults the gauge to empty, and disables the transfer pump. The PCM/powertrain control module(engine computer as most call it) monitors the level in both tanks, when it detects the fuel level in the front tank drop to below 75%, it turns the rear transfer pump on to move fuel forward, when the fuel level in the front tank goes above 75%, it turns the pump off. If the PCM doesnt see the fuel level in the rear tank drop proportionately to the rise in the front tank(also accounting for fuel used), it assumes there is a problem, and disables the system. The relay in your underhood fuse panel for a gas engine should be for the front fuel pump for the engine, and there should be a secondary fuel pump relay clipped on or near the fuse panel. If its a diesel, the relay inside the panel is for the rear transfer pump.

The PCM also uses the info from the senders to figure the total remaining fuel left, and sends that info to the cluster for the fuel gauge.

This is all assuming you have a factory system and not an aftermarket one.
 
THEFERMANATOR said:
No, the PCM controls it all on yours. If any fault is detected in either sender or the rear pump doesn't transfer fuel, the PCM defaults the gauge to empty, and disables the transfer pump. The PCM/powertrain control module(engine computer as most call it) monitors the level in both tanks, when it detects the fuel level in the front tank drop to below 75%, it turns the rear transfer pump on to move fuel forward, when the fuel level in the front tank goes above 75%, it turns the pump off. If the PCM doesnt see the fuel level in the rear tank drop proportionately to the rise in the front tank(also accounting for fuel used), it assumes there is a problem, and disables the system. The relay in your underhood fuse panel for a gas engine should be for the front fuel pump for the engine, and there should be a secondary fuel pump relay clipped on or near the fuse panel. If its a diesel, the relay inside the panel is for the rear transfer pump.

The PCM also uses the info from the senders to figure the total remaining fuel left, and sends that info to the cluster for the fuel gauge.

This is all assuming you have a factor y system and not an


Yes the relay under the hood in the compartment is for the front tank. It is a gas engine. Yes it is all factory . Did not see any relay for the rear tank will have to look again. It is defiantly not in that compartment with all the other relays, that would just make too much sense! What do you think the problem is , the relay or the PCM ? And also where is the PCM located ?
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The pcm is located next to the drivers side battery if I'm not mistaken. There's no telling what is wrong without putting a scan tool on it and diagnosing it. This is NOT a throw parts at it problem unless you like throwing money away(if you do, throw it my way). There is no diagnosing this system without some special tools. You need to see what the PCM is seeing for fuel level, try and actuate the transfer pump, and go from there. It could be a stuck float 8n either tank, failed sender, corrosion on a sender, broken wire, bad relay, failed pcm, nobody knows without diagnosing it. The only thing I can day is I know there was a tsb regarding the rear tank float sticking, but it was for diesel models.
 
GM Guy said:
@Fermanator, when in GMT800 did the PCM control start? From the beginning in 2001, or later?
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I really do not know. At least by 03 it was, before then was hit or miss. My 01 donor truck still had the ignition switch triggering the starter relay, but others 01's had the ecm control it.
 
THEFERMANATOR said:
The pcm is located next to the drivers side battery if I'm not mistaken. There's no telling what is wrong without putting a scan tool on it and diagnosing it. This is NOT a throw parts at it problem unless you like throwing money away(if you do, throw it my way). There is no diagnosing this system without some special tools. You need to see what the PCM is seeing for fuel level, try and actuate the transfer pump, and go from there. It could be a stuck float 8n either tank, failed sender, corrosion on a sender, broken wire, bad relay, failed pcm, nobody knows without diagnosing it. The only thing I can day is I know there was a tsb regarding the rear tank float sticking, but it was for diesel models.
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I think it was the rear float stuck , the person who drives the truck was only filling the front tank and not filling the rear one. I put it all back together and it seems to be working??? Who knows time will tell I guess. Thanks for the help.
 
We are struggling to diagnose this problem. 2001 3500, gas. Both pump assemblies have been changed. But the gauge, usually, won't read. It's triggering a code P0461 about the fuel level sensor. But it doesn't matter which pump it still gives the code. (We've switched back and forth to rule out faulty pump) when the code is cleared the rear pump will start working until the code returns after a few minutes.
Using the scanner we see the computer is reading the appropriate fuel levels but the information is not getting to the gauges. We even switched out the instrument panel with another truck we have here. It works fine in the other truck, neither fuel gauge worked on the problem truck. Have followed the steps in this post checking the voltage on the wires and checking grounds. Everything seems fine.

Also is seems there is no balance module or vcm this truck.
 
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bluberryfrog said:
We are struggling to diagnose this problem. 2001 3500, gas. Both pump assemblies have been changed. But the gauge, usually, won't read. It's triggering a code P0461 about the fuel level sensor. But it doesn't matter which pump it still gives the code. (We've switched back and forth to rule out faulty pump) when the code is cleared the rear pump will start working until the code returns after a few minutes.
Using the scanner we see the computer is reading the appropriate fuel levels but the information is not getting to the gauges. We even switched out the instrument panel with another truck we have here. It works fine in the other truck, neither fuel gauge worked on the problem truck. Have followed the steps in this post checking the voltage on the wires and checking grounds. Everything seems fine.

Also is seems there is no balance module or vcm this truck.
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None of the balance module info applies to your truck. It is all controlled via the pcm. The pcm must see the rear level drop and the front raisr or hold, otherwise it defaults to empty. The cluster has zero influence, its sll in the pcm.
 
Does the PCM also control the secondary pump in a 2003 8.1L Gas C4500? I can't find the module
 
Welcome to the forum MFD.
I know nothing about the problem You are having.
There would most likely be a greater response if You started a new thread on the matter. Oh yeah, some will be asking for pics too. 😹
 
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