Fuel system

[JMR]

Hi all,
I’m from Zimbabwe, I drive a Nissan patrol 2007 TD42 pick up. I’m having a problem with my sub tank not pumping into my main tank any advise would be greatly appreciated.
It pumped for about 15min then the sub tank light came on and the fuel gauge dropped to empty.
The pump is working, I wired it direct to the battery and it pumped fine. Is there a sensor that may be gone or is it the fuel float/sender unit that’s gone?
I was driving on a very corrugated road when this happened!
Many thanks in advance for any advise you can give me regards to this.
Cheers for now

[the evil twin]

It will be the faulty Sender Unit causing the issue.
The Sub Tank Computer monitors the Sub Tank Sender, Main Tank Sender, Pump, Wiring and Switch
If that Fault Lamp is illuminated the Pump is electrically isolated by the Computer

First, disconnect the Battery for 10 minutes to reset the Sub Tank Computer.
If the Sub Tank Fault Lamp stays out (it will go out for a short period and do a self test) then that is great.
If the Lamp comes back on after the self test then you will need to replace the faulty component.

[Cremulator]

I just had this issue with the sub tank light staying on three days ago. I disconnected the main battery for 10 minutes and the sub tank light stayed off when I started the car the next time.
Thanks for the tip Evil Twin.

As a side question, does the sub tank ever engage automatically, like when the fuel warning light has been on for the main tank for any period? Or is it just triggered manually with the push button switch on the dash?

I filled my sub tank in November 2018 and it has been dropping slowly. The needle is sitting at half full now after 10 months.
I run my main tank to empty before refueling each time and I've filled the main tank exactly 10 times since filling the sub tank.

[Hodge]

I just had this issue with the sub tank light staying on three days ago. I disconnected the main battery for 10 minutes and the sub tank light stayed off when I started the car the next time.
Thanks for the tip Evil Twin.

As a side question, does the sub tank ever engage automatically, like when the fuel warning light has been on for the main tank for any period? Or is it just triggered manually with the push button switch on the dash?

I filled my sub tank in November 2018 and it has been dropping slowly. The needle is sitting at half full now after 10 months.
I run my main tank to empty before refueling each time and I've filled the main tank exactly 10 times since filling the sub tank.

My understanding is there is a bit of fuel pumped from sub every time vehicle is started and is automatically transfered when fuel light comes on.

Just out of interest , why are you not using the sub fuel that much ? Don't drive enough or always only fill the main ?

[the evil twin]

Wot Hodge said ^^^^

Every time you start the vehicle the sub tank does a self test of the pump IF there is fuel in the sub AND the main is below 3/4's full.
Each time it does the test it will pump up to 1/4 litre of fuel which soon adds up.

[Cremulator]

That's good to know that the sub tank pumps a little each time you start the car under certain circumstances.
@Hodge I filled the sub tank when we went camping last year and haven't been using the sub tank because I don't drive much or long distances, but mainly because I've been logging my full ups to monitor fuel consumption and want to keep consistency of milage from the main tank.
Since removing the full length roof rack the fuel consumption went from 14.66l/100km on the previous tank (with an average of 15.067l/100km over 10 tanks) to 13.68l/100km.

[Cremulator]

I might have spoken too soon on the sub tank light fix. After a short drive today it's come back on.