Hi, Newby here and not owned a Ford since my 2.0 Ghia Sierra way back when.. Just bought an 18 plate Grand tourneo Connect with the disability conversion to make life easier getting our two Golden retrievers in and out of the car  and after bringing it home, went to fill up with diesel and noticed the gauge only registered halfway between 3/4 and full.. Gave it some thought and rung the company who did the disability conversion and as I suspected they put a smaller fuel tank in to allow for the dropped floor etc.. New tank is 54 litres.. Got in touch with my local Ford dealership but the only thing they can do apparently is to adjust the range to fill up parameter? Given everything is electronic these days, I`d have thought changing the parameters on the sender unit would be relatively straight forward, but apparently not. I wondered if the wealth of experience on here could tell me differently or offer any solution?

Any help appreciated..

Andy

20 hours ago, Scubasad said:

Given everything is electronic these days, I`d have thought changing the parameters on the sender unit would be relatively straight forward,

The sender unit is a physical item, not electronic. It is simply a float connected to a variable resistor.

I don't quite know why changing the size of the tank would alter the operation of the sender unit, the float will still be at the top when the tank is full, and at the bottom when the tank is empty it has no idea what the capacity of the tank is.

Of course if the sender has been damage when it was moved in to the new tank then that would account for the inaccurate reading. My thoughts would be either the float has a hole in it and has got some fuel inside or that the float arm is bent or catching on something.

The float sensor may just be a rheostat (variable resistor) but these days the way the signal is processed is a bit more complex.

This is because the fuel tanks usually have an irregular shape. The rheostat generates a linear resistance depending on the float position. This however does not accurately reflect the actual content of the fuel tank.

To be accurately able to display the actual content of the fuel tank the fuel tank capacity is configured in the vehicle configuration. Based on the configured fuel tank capacity the electronic module that processes the rheostat signal (depending on engine type and Ford model this can either be the instrument cluster, BCM or PCM) calculates the actual content of the fuel tank. Next to the rheostat signal, other factors like actual fuel consumption and average fuel consumption are also part of the calculation. 


Because of this you cannot just install a different capacity fuel tank without changing the vehicle configuration. Also important is the fact that the available configuration parameters are usually limited to and based on the factory fitted fuel tank capacities and dimensions.


To be able to determine what is actually going wrong the following is important to know:

* What fuel tank is actually fitted. Is this an original Grand Tourneo Connect fuel tank of the same Year and model.
* What fuel tank capacity is configured.
* What fuel senser unit is fitted. Is this the original Grand Tourneo Connect unit and does it match the fitted fuel tank.

 

23 hours ago, unofix said:

The sender unit is a physical item, not electronic. It is simply a float connected to a variable resistor.

I don't quite know why changing the size of the tank would alter the operation of the sender unit, the float will still be at the top when the tank is full, and at the bottom when the tank is empty it has no idea what the capacity of the tank is.

Of course if the sender has been damage when it was moved in to the new tank then that would account for the inaccurate reading. My thoughts would be either the float has a hole in it and has got some fuel inside or that the float arm is bent or catching on something.

Fully appreciate that, but if the fuel gauge is calibrated for what I assume would have originally been a 60 litre tank then there must be a way to recalibrate the fuel gauge to recognise a 54 litre tank. If they can reset the distance to next fill parameter you would assume logically that the gauge operates in a similar fashion?

22 hours ago, JW1982 said:

The float sensor may just be a rheostat (variable resistor) but these days the way the signal is processed is a bit more complex.

This is because the fuel tanks usually have an irregular shape. The rheostat generates a linear resistance depending on the float position. This however does not accurately reflect the actual content of the fuel tank.

To be accurately able to display the actual content of the fuel tank the fuel tank capacity is configured in the vehicle configuration. Based on the configured fuel tank capacity the electronic module that processes the rheostat signal (depending on engine type and Ford model this can either be the instrument cluster, BCM or PCM) calculates the actual content of the fuel tank. Next to the rheostat signal, other factors like actual fuel consumption and average fuel consumption are also part of the calculation. 


Because of this you cannot just install a different capacity fuel tank without changing the vehicle configuration. Also important is the fact that the available configuration parameters are usually limited to and based on the factory fitted fuel tank capacities and dimensions.


To be able to determine what is actually going wrong the following is important to know:

* What fuel tank is actually fitted. Is this an original Grand Tourneo Connect fuel tank of the same Year and model.
* What fuel tank capacity is configured.
* What fuel senser unit is fitted. Is this the original Grand Tourneo Connect unit and does it match the fitted fuel tank.

 

I have no idea if it is a genuine ford tank, all I know is that it`s 54 litres. I obtained this detail from the coachbuilders who originally carried out the disability conversion. I`ll try calling them again on Monday and see if they can offer any furthe information.. The fact that the vehicle is 7 years old and never been adjusted to match the tank makes me wonder if it is actually possible or not.. I`ll ask if the original sender unit was used or if it`s an aftermarket one.

I don't think many people fill tanks to the brim nowadays, so previous owner(s) may never even have noticed.

On 10/5/2025 at 11:48 AM, Scubasad said:

Fully appreciate that, but if the fuel gauge is calibrated for what I assume would have originally been a 60 litre tank then there must be a way to recalibrate the fuel gauge to recognise a 54 litre tank.

There is, but that is not the problem you have.

If you move the float arm fully to the top then the gauge will always read full. Likewise when the float is full to the bottom the gauge will always show empty. The capacity of the tank is irrelevant.

For your gunge to be showing between three quarters full, and full must mean that the float is not reaching the top for some reason. Now it is possible that they have fitted a different sender unit to the new tank and the resistance of that new sender is not the same. If that is the case then the system needs recalibrated. However, as @JW1982 has already said there is not the option of an infinite selection. There is a drop-down menu of possible tanks that may be fitted to your vehicle, if the option for your tank is not there then that makes fixing the problem a bit more difficult.

9 minutes ago, unofix said:

There is, but that is not the problem you have.

If you move the float arm fully to the top then the gauge will always read full. Likewise when the float is full to the bottom the gauge will always show empty. The capacity of the tank is irrelevant.

I'm not sure that is 100% correct.  The arm pivot is attached fairly high up on some senders (as seen in your picture).  There may not be enough space for the full arc of the arm before the float hits the top of the tank.  Senders are slightly adjustable in height so that they always sit on the bottom of the tank.  The top section can move up & down a bit to take up the slack.  Not sure if that has happened here, but I think it would be a possibility. 🤔

1 minute ago, TomsFocus said:

I'm not sure that is 100% correct.  The arm pivot is attached fairly high up on some senders (as seen in your picture).  There may not be enough space for the full arc of the arm before the float hits the top of the tank. 

I think you missed my original post.

On 10/4/2025 at 12:17 PM, unofix said:

My thoughts would be either the float has a hole in it and has got some fuel inside or that the float arm is bent or catching on something.

The thing is, if the float can move fully to the top then the gauge will read full, irrespective of the capacity of the tank. If for some reason the float is being prevented from moving fully then of course it will not show the tank is full even when it is.

I have just received the following from the coach builders : 

I have just spoken to one of our engineers in the R&D department regarding your below question and I have been advised that, the OEM arm is used to measure the fuel level in the reduced tank. Due to the reduced fuel tank, the OEM arm doesn’t register fuel to the top of the full level.

 

The fuel gauge does read correct but will only show the ¾ full on the fuel gauge.

 Whether this makes any difference or will allow anything to be done, I have no idea..It does make me wonder if there is some diagnostic tool that can alter the parameters from a 60 litre to a 54 litre tank so that the gauge actually shows full when the tank is full rather than between 3/4 and full

On 10/6/2025 at 5:25 PM, Scubasad said:

The fuel gauge does read correct but will only show the ¾ full on the fuel gauge.

 Whether this makes any difference or will allow anything to be done, I have no idea..It does make me wonder if there is some diagnostic tool that can alter the parameters from a 60 litre to a 54 litre tank so that the gauge actually shows full when the tank is full rather than between 3/4 and full

That's very interesting, so it seems the new tank is shallower and thus the movement of the float arm is restricted and can't move high enough to reach the top of the variable resistor.

A recalibration of the gauge could potentially partly fix the issue but will probably introduce an inaccuracy across the range meaning the only time the gauge would be fully correct is when the tank is empty and when it is full.

https://forscan.org/forum/viewtopic.php?f=16&t=14698

An alternative fix would be the reshaping of the float arm (make the arm shorter). However I suspect that would involve a lot of trial and error in order to get a full sweep of the variable resistor, and thus the gauge with less move movement of the the float.