sub tank indication

[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.Subtankswitch.pdf

[Wizard52]

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

Startupdashlights.pdf

[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.