Fuel Gauge always full

[darkyellow]

Hi All,
New to the forum as per my intro.

Issue is that the Father in law just purchased a Gregory's 1998 - 2011 manual that does not contain the info we require.
Before posting, I have spent hours searching the web for info - to no avail !!!!

The problem is

1. The Main fuel tank gauge reads full, regardless of the quantity of fuel in the tank.
2. The Sub tank reads correctly
3. Sub-tank light on the dash remains lit

We have tried disconnecting the battery and waiting - no change
We have tried running a new earth to the chassis - no change
We have pulled the sender unit from the tank and checked all signals. - all OK. Sender unit output 5ohms (full) - 80 ohms ( empty)

This model does not use the low fuel sensor, but ( I am guessing) uses the actual sender unit as the determining factor - which, when the tank is low, works, ie shows the fuel warning light

Does anyone have a wiring diagram for this vehicle.

Specifications are

2003 GU3 TI
4.8L petrol



Thanks in advance

Dave

[the evil twin]

Hi All,
New to the forum as per my intro.

Issue is that the Father in law just purchased a Gregory's 1998 - 2011 manual that does not contain the info we require.
Before posting, I have spent hours searching the web for info - to no avail !!!!

The problem is

1. The Main fuel tank gauge reads full, regardless of the quantity of fuel in the tank.
2. The Sub tank reads correctly
3. Sub-tank light on the dash remains lit

We have tried disconnecting the battery and waiting - no change
We have tried running a new earth to the chassis - no change
We have pulled the sender unit from the tank and checked all signals. - all OK. Sender unit output 5ohms (full) - 80 ohms ( empty)

This model does not use the low fuel sensor, but ( I am guessing) uses the actual sender unit as the determining factor - which, when the tank is low, works, ie shows the fuel warning light

Does anyone have a wiring diagram for this vehicle.

Specifications are

2003 GU3 TI
4.8L petrol



Thanks in advance

Dave

Sounds like a short cct to earth on the wire to the main tank gauge or a faulty main tank gauge.
Is it reading full or off scale high?
A fault like that will cause the sub-tank computer to fault out and illuminate the dash light.

[darkyellow]

Mmm...Off scale full ( main tank) when the sender unit is connected and was thinking that its indicative of a short.
Checked as much of the wiring as we could.

Found the sub tank control board ( under dash) all "looks ok", no brown smells.
eyeballed the circuit board - no apparent issues etc.

Tried running another earth to no avail.

Really need a wiring diagram now to start checking the I/p O/p voltages etc for the sub tank control board.

( or find some parts to swap !!!)


Regards
Dave

[happygu]

Dave,

Follow the wiring back into the cab if you can, and then disconnect from any internal parts or circuits, and then check sender and wiring together from under the truck ..... that will eliminate a short in the wiring underneath and let you know if it is something in the control circuit

[darkyellow]

Thanks guys,
Have traced all wiring back to the sub tank control board and checked all voltages etc, which appear quiet normal.
Sub tank switch operates, and I can see variance on the inputs from the sender units with changes in (effective) fuel level
No shorts to be measured at all.


However, may have stumbled on an issue.
While checking the battery, its was down to 12V ( rather than a healthy 13.8) and the Father in-law recalls that this issue started when the battery was replaced.
Have thrown the battery on charge, and does not seem to be taking a charge beyond the 12.0V


Off to buy a new battery.....

Will keep you updated !!!

Regarsd
Dave

[Shummezz]

Hi Guys,

I have a similar issue. My 91GQ fuel tank drops from full but never gets lower than 1/4. Does anyone have instructions as to how to drop and clean the tank and service the fuel sensor?

Cheers, Chris

[BigRAWesty]

Hi Guys,

I have a similar issue. My 91GQ fuel tank drops from full but never gets lower than 1/4. Does anyone have instructions as to how to drop and clean the tank and service the fuel sensor?

Cheers, Chris

Under the carpet / vynal in the rear you'll find a round hatch screwed down to the floor..
Lift that plate and that will give you direct access to the fuel pickup.

If you want to drop it syphon the fuel out and undo the fuel sender plug.
Under the wheel Arch you'll find a plastic cover over the fuel hoses..
Remove that and then remove the fill pipe from filler hatch..
Then from under the car you'll see bolts that hold the gaurd up and once that's gone I'm pretty sure it's 3 bolts along the front and 3 at the rear and it's coming out..