More Sub Tank Issues

I have read the past posts and suggestions about this problem.
I have a 2005 4.8 TI. I've put new earth straps on and have disconnected the battery a couple of times. It sometimes works but after a while the light comes one and I am unable to transfer fuel.
Is this likely to perhaps also be a fuse, and if so can anyone tell me which fuse it is?
Has anyone thought of placing a fuel transfer pump between the main and sub??

I would appreciate any assistance before I take the truck to an auto elec.....thanks....LA

I have spent this afternoon pulling the control switch out and disconnecting as one suggested in a forum. Still no luck...LA

Yendor is your man he wont be too far away

I don't think it will be a fuse.

Do both fuel gauges work correctly? this is very important.

Have you installed long range tanks?

When it "sometimes works" can you see the fuel being transferred when you look down the main fuel filler pipe?

Hi Yendor.....yes I have installed a 160 ltr main tank. I have not seen the fuel transfer apart from seeing the gauge on the sub go down when it works. The gauge in the main tank is not accurate, but the sub tank has worked when the long range tank has been in....I'm wondering whether it would be easier to install a manual switch to transfer the fuel. Have you heard of this being done before.....cheers....LA

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Originally Posted by LALAW

Hi Yendor.....yes I have installed a 160 ltr main tank. I have not seen the fuel transfer apart from seeing the gauge on the sub go down when it works. The gauge in the main tank is not accurate, but the sub tank has worked when the long range tank has been in....I'm wondering whether it would be easier to install a manual switch to transfer the fuel. Have you heard of this being done before.....cheers....LA

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That's up to you.........if your transfer pump is not faulty, all you would need to do is mount an on/off switch in the dash, wire up a relay to run the transfer pump and then remember to turn it off before the sub tank ran out of fuel.

If the low level fuel sensor is still working in the sub tank we might be able to make it an automatic shutoff.

Thanks mate......I think due to the inconsistency in the sub tank, I would prefer to have a manual override.
By any chance would you have a wiring diagram or be able to advise which one I need to tap into....cheers....LA

First thing you need to do is test that your transfer pump is working.

There are two places you can do this

1. At the control module located below the radio (this would be the easiest place to wire in the manual switch) or

2. The connector on top of the sub tank, access is via an inspection cover found under the carpet.



To test at the control module, disconnect the connector at the control module. The Red wire should have power when the ignition is on and the Green with black trace wire goes to the fuel pump. With some wire join the Red and Green with a black trace wires together. You should be able to hear the fuel pump run and if you remove the main fuel filler cap and look down the pipe you should be able to see fuel coming out.


To test at the fuel tank, run a temporary wire from the positive of the battery and connect it to the Green with a black trace wire. you should be able to hear and see the fuel pump working as per above.

If the fuel pump is working all you will need to get is a 12 volt relay and an on/off switch. It would also be a good idea to get a switch that has a warning light when it is on or even get a separate warning light or buzzer.

Also if you do test the fuel pump by disconnecting the control module can you see if the fuel gauges still work correctly when you turn the ignition on.

Let me know how you go with testing the pump. If it test ok I will then go through it with you how to wire up the manual switch.

Thanks for your help.....I'm away this weekend and will have a go and report back after next weekend.
Thanks again Yendor......LA

Hi Yendor,
I have located the wires.
The colors are:- green with grey stripe
Two black with grey stripes
Two blue with grey stripes
One white with grey stripes, which is possitive when the ignition is on.

I connected the white to the green and blew the ign 10 amp fuse. (No. 28 ) on the fuse box.

After replacing the fuse I turned on the ignition and heard both the pump and fuel being drained into the main tank.

It then stopped working.

I removed the cover under the back seat. There are two plugs which go into the sub tank. The plug towards the front of the truck has a pos & neg. when these are directly wired to the power and earth, the sub tank pump kicks in and the tank drains.

For some reason now the sub tank fuel gauge is not working....it is showing full, even though the tank is empty.

Had enough time for a beer......LA

Those wire colors are different to the wiring diagram I have.

Does the sub tank gauge still read full when both plugs are disconnect at the sub fuel tank?

It sounds like the transfer pump is working ok.

Yendor......yes the sub tank reads full when both plugs are disconnected.....cheers....LA

If the sub tank gauge still reads full with both the plugs disconnected you more then likely have a short to ground in the wire between the gauge and the sub tank.

Start by following the harness from the sub tank to the dash looking for any signs where the harness might be rubbing on a metal surface or has been caught/pinched somewhere.

The harness runs along the top of the sub tank towards the rear of the vehicle, then across the chassis support brace at the rear of the sub tank then down the LHS chassis rail to a connector in a black plastic box mounted on the chassis rail below the passengers from seat. Try disconnecting these connectors and see if the fuel gauges drops.

From there the harness runs up through a grommet in the floor under the passengers front seat and down under the LHF scuff plate and up into the dash.

Thanks again mate......another job for the weekend. I will let you know how I go.

If this does not work, I may just put in an inline switch and drain the tank manually remembering when it's full or empty....cheers....LA

Hi Yendor....... Manual switch is in and appears to be working well. I even think the sub tank is reading accurately but will check this out next weekend when we are in the bush.....cheers......and thanks for your assistance.....LA