sub tank indication

[cookster]

Hi new to this. just bought a 2003 GU and my sub tank light is always on. Filled both Main & sub tanks. and have used 3/4 of main tank fuel, but sub tank has not moved and light is still on. ANY ideas "Cookster"

[macca86]

Post an intro first. If the sub light stays on that indicates a fault with the sub tank. The sub tank on patrols transfers into main tank rather than fuel the engine. It should transfer a little on start up every time once your main tank is 3/4 to half full

[Yendor]

Try disconnecting the battery for half an hour. If this turns off the light you will need to run an extra earth lead to your chassis.

[Sanpeter]

Just had the same problem. Found elsewhere it could be an earth problem, it could be that the sub tank was overfilled or it could be the sub tank processor.
Anyway the easy answer, which worked for me and lots of others is just disconnect your battery for 5 - 10 mins.
All is working fine now.

[MEGOMONSTER]

Try disconnecting the battery for half an hour. If this turns off the light you will need to run an extra earth lead to your chassis.
Extra earth from subtank to chassis. It seems I have this same problem now.

Light is on button but not transferring.
I have disconnected the battery already. Which I thought fixed it, but then subtank light on dash came up.
So I disconnected again, dash light is off but still not transferring.

But it does give a sprinkle into the main tank everytime I start it.

I can hear the transfer motor werrrrrring but not fill the main tank.

[Winnie]

If you take the fuel cap for the main tank off can you see fuel flowing?

[MEGOMONSTER]

If you take the fuel cap for the main tank off can you see fuel flowing? Only a trickle on start up. But not by hitting the sub tank button.

[Dananjen]

Hi All, I have a similar issue in my 2002 GUIII,

I have recently fitted new stereo and UHF, prior to fitting these, I had no "subtank dash light" on, but now it is of yet feeding from the main tank. I have tried pushing the button on the dash, and this doesn't turn the dash light off. I haven't touched this side of the wiring, Could it be a faulty button in the dash ??

[boots]

Try removing the fuse first check and replace or put back in. Second disconnect the battery for a while then reconnect to see if the light goes out .

[the evil twin]

Hi everyone... OK... the old "sub tank light" issue once again eh.

First off the warning light has nothing to do with the Sub Tank switch as such IE it will tell you if it is faulty but operating the switch does bugger all if the warning light is illuminated.

Secondly the warning light should latch once there is a fault detected even if the fault goes away.
People have told me that isn't always the case but so far I have always found it to be so (just sayin' is all).

Third, you need to check fuses 24 and 27 (bottom 2 fuses first row) and 28 (bottom fuse second row)

After all that... to reset the system and extinguish the warning light, erase the fault codes and reset the latch you need to disconnect the battery ground or unplug the sub tank control box.

Before you do that it is a good idea to do one of two things
a) run an earth from the sub tank to chassis
OR
b) read the fault codes so you know what it "thinks" is wrong
So if the warning lamp is illuminated.
Turn the ignition off
Turn ignition on
Press the Sub Tank switch On and Off at least 5 times in quick succession
The light should then flash on and off every two seconds (if it doesn't try again quicker or slower)
Once it is flashing wait at least 10 seconds then start the engine, now it gets interesting...
You should see 4 or 5 very quick flashes (this indicates the control unit or computer if you prefer is latched and has codes)
You will then have a long pause (a few seconds) then a long flash ( a few seconds)... get ready
The next flash will be a medium (approx 1/2 second) then 1 or more short flashes if you get another medium flash then more short ones that is a second fault
1 medium and 1 short means the fault is in the main fuel tank full sensor or wiring
1 medium and 2 short - sub fuel tank sender or wiring
1 medium and 3 short - no pump power
1 medium and 4 short - pump wiring

Now, if the fault has disappeared and you reset the warning light then happy days

If you disconnect the battery ground to reset the control box and the warning light illuminates after a short time (other then for ign on bulb test) then it means you still have a fault detected you can either fault find or bite the bullet and fit an extra earth wire between tank and chassis which probably has about an 80% success rate

If you fit the strap, then disconnect the battery ground and the light still illuminates after a short time then you need to sort out fault codes.

Bottom line is this... you can fix the fault or have a fault disappear but until you disconnect the battery the controller will not (or at least should not) extinguish the light which means the sub will self test depending on the fault but will not transfer fuel on demand IE if you look down the tank filler you may see fuel transfer during the test period of a minute or two but you wont see fuel transfer when you press the button

Sorry for the long post but hope that helps at least some people

[Dananjen]

Thanks, I disconnected my battery and appears to have solved the issue, however I do have another, but believe it is the EGR issue

[Cuppa]

I have a slight twist on this issue, but first a question to ET. Should I expect the flashing codes on my ’06 4.2 TDi or is this only applicable to later models with more computer control?

When I switch on the sub tank, the switch light illuminates & the fuel is pumped from the sub tank to main tank. When the sub tank is finally empty the switch light goes out. All good so far.
However, although it did when I first got the vehicle, I no longer get the short illuminating/pumping when first switching on the ignition. The amount of fuel in the main tank makes no difference. Extra earths were fitted (which successfully resolved dash instrument issues I had after fitting additional batteries in the pod & earthing them to the chassis). The lack of the ‘test pumping’ when ignition is turned on doesn’t really seem to be any consequence so I haven’t worried about, but in light of this discussion it’s got me wondering about it again.
Could this result from my habit of completely filling my sub tank & then pumping from it when the main tank is almost empty & transferring it’s contents until the sub tank is dry?

I just went to check in the car. Sub tank shows completely empty on the gauge. Main tank about ¾ full. Switched on ignition - no sub tank light. Pushed sub tank switch in. Light illuminated & I could hear the transfer pump working, but switched it off quickly as I could tell from it’s sound that it was running dry.

[the evil twin]

I have a slight twist on this issue, but first a question to ET. Should I expect the flashing codes on my ’06 4.2 TDi or is this only applicable to later models with more computer control?

When I switch on the sub tank, the switch light illuminates & the fuel is pumped from the sub tank to main tank. When the sub tank is finally empty the switch light goes out. All good so far.
However, although it did when I first got the vehicle, I no longer get the short illuminating/pumping when first switching on the ignition. The amount of fuel in the main tank makes no difference. Extra earths were fitted (which successfully resolved dash instrument issues I had after fitting additional batteries in the pod & earthing them to the chassis). The lack of the ‘test pumping’ when ignition is turned on doesn’t really seem to be any consequence so I haven’t worried about, but in light of this discussion it’s got me wondering about it again.
Could this result from my habit of completely filling my sub tank & then pumping from it when the main tank is almost empty & transferring it’s contents until the sub tank is dry?

I just went to check in the car. Sub tank shows completely empty on the gauge. Main tank about ¾ full. Switched on ignition - no sub tank light. Pushed sub tank switch in. Light illuminated & I could hear the transfer pump working, but switched it off quickly as I could tell from it’s sound that it was running dry.

Hiya Cuppa,

I would think yours should show the fault code 'flashes' the same as mine.
Mine is a series 1 and I am reasonably sure (reasonably but not 100%) that it is the same sub tank controller in all the GU TD42T iterations.

Your reference to switch light (green) illuminating when you first got it throws me a tad as I have never noticed that on any of my rigs so possibly there are differences.
The warning light (amber) should illuminate when first switching on as it is part of the bulb warning circuit and main tank or sub tank fuel level makes no difference.

If you want to check for sure if your vehicle is doing the test pumping, have a 1/2 tank or less in the main, take the filler cap off, switch the ign to on and quickly look down the filler neck to see if there is fuel flow.
The '1/2 tank in the main' is to make sure the main tank full sensor isn't set.

Your habit of fuel mangement is exactly the same as mine so that shouldn't matter.

The last bit throws me a little bit as the factory sub tank setup has a sensor that tells the pump to stop when the sub is empty but possibly you are turning the pump off quicker than the sensor is triggering the controller.
Again I would check to see if there is flow into the filler neck and maybe give it 1 minute or so.
If there is no flow and the pump continues running with no fuel in the sub then there is a fault.
The sub tank pump uses fuel flow for cooling but a minute or less running shouldn't hurt it.

[Cuppa]

Thanks ET, I’ll check it again when I have less fuel in the main tank.

I think I did switch off the sub tank pump this morning before the sensor had a chance to switch it off. Normally the sensor would do this if I’d left it. I only switched it off myself because, being half in, half out the car & without the motor running I could easily hear the pump running dry.

I have never seen an amber light on the switch, only the green one.

[the evil twin]

Thanks ET, I’ll check it again when I have less fuel in the main tank.

I think I did switch off the sub tank pump this morning before the sensor had a chance to switch it off. Normally the sensor would do this if I’d left it. I only switched it off myself because, being half in, half out the car & without the motor running I could easily hear the pump running dry.

I have never seen an amber light on the switch, only the green one.

My bad... should have explained it a tad better
I know that you are aware of most of this but for others wh may not be...

Green light - in the sub tank selector push button switch
Steady illumination when selected, fuel transfer conditions are met and the sub tank pump is energised and transferring fuel
Flashes codes if the Sub Tank test function is activated (Ign on, cycle sub tank switch minimum 5 times, start engine)

Amber light - sub tank warning light in the instrument cluster
Engine off - Steady when Ign is turned on and bulb test circuit is active then off when engine started
Engine running - should be off but illuminates Steady when a fault is detected by the Sub Tank Controller (latches on and inhibits sub tank operation, reset by disconnecting battery earth)

[Cuppa]

I was just about to post to say that the amber dash light must be one of those things, like the low fuel warning light, that DX owners have to manage without........ but just before hitting the send button a little voice told me to go & check. Well of course it turns out that I do have an amber sub tank light in the dash! Doh! I suppose because I never actually knew it’s function previously & the sub tank transfer was working, I just didn’t take much notice of it. Now I know what it’s for.......... & it works just as you said.

Can anyone tell me if there is an owners handbook among the manuals here suitable for my vehicle. It might be handy to know what other lights there are in case any light up at some point.

[Wizard52]

Hi Cuppa

I have attached a copy of the original owners manual.50568

[Wizard52]

Also I have attached copy of owners manual page showing start up light procedure.

50569

[Cuppa]

Thanks muchly Wiz.

EDIT: I actually found at I do have an owners Handbook after all. It’s been that long since I’d seen it I’d forgotten I had it. Doh!

Anyway all lights working as they are supposed to, except Sub tank switch light (green) doesn’t come on when ignition turned on. It used to. I’m now assuming that all is probably well, & the reason it’s not coming on is that I have a tad over ¾ full in main tank & sub tank is empty. Will check when I get more fuel.

I thought initially that the water in fuel light wasn’t working, but then sussed that in the TD42i that the ‘enginge malfunction’ light doubles as the water in fuel light.

Also learned that the oil pressure light should not be used as an indicator of low oil. (oil level was spot on though).

[Nixon]

Thanks Evil, you have just confirmed that I am dangerous under the bonnet of a 4wd. It recently cost me $171 to sort out the above problem and they couldnt find anything wrong ! Just reset the system, & I note that my clock (Eg battery) had been off for a couple of hours - probably easy money. You have also opened up a new world for me to work out what all these codes & flashes are !! Have also heard that guys are buying a diagnostic device that gives you some idea if the fault is electrcal or mechanical - probably would just increase my danger level.

[Nightjar]

Would "Cookster's" 2003 Patrol have a computer?
Had a similar problem with my 2002 and the problem was, my main/starting battery had karked it, and unbeknown at the time, the auxiliary battery was both my main & auxiliary.
My system has a solenoid separating the two, and most of the add ons run from the auxiliary in ign accessories position.

[Cuppa]

Yesterday I filled both tanks & following this the sub tank warning (orange) light came on & stayed on. Drove 20kms, switched off & then started the vehicle again. Warning light still on.

This morning I did two things. 1. Siphoned 5 litres out of the sub tank as I seem to recall reading somewhere that over filling can make the warning light come & 2. disconnected battery for a while. It worked, no warning light now.

Of course I don’t know if siphoning the fuel out was part of the ‘cure’ or not but assuming the initial cause of the warning light staying on was over-filling the sub tank can anyone explain how & why this happens? I’ve previously filled both tanks right up to the filler cap & this has not occurred. ???

[the evil twin]

Hiya Cuppa

1 - If the fault light comes on it latches IE you can turn the vehicle off for weeks but the light will still illuminate next time you start it until you remove power (battery/fuses/unplug computer)

2 - I think the fault was temporary gremlin and may not return

[Cuppa]

Hiya Cuppa

1 - If the fault light comes on it latches IE you can turn the vehicle off for weeks but the light will still illuminate next time you start it until you remove power (battery/fuses/unplug computer)

2 - I think the fault was temporary gremlin and may not return


Hi ET,
1. I read that in one of your previous posts & found it useful. That’s why I disconnected the battery.

2. Gremlins are little bastards aren’t they!