Fuel gauge showing incorrect reading help pls

[matt123]

Hello All

I have a Mercedes ML 350 W164. Beautiful machine when all is well.

I have a problem my fuel gauge is showing up incorrect. I filled up 2 weeks ago driven 100+ miles or so and the fuel gauge is staying between full and just slightly under full.

It’s not showing the correct reading does anyone have any idea as to what this can be?

 

[John Laidlaw]

Welcome! Could be a float sensor but a Star diagnostic should tell

 

[Big Cheese]

Check rear sam for water damage,if your spare wheel well is damp that could be your problem.

 

[matt123]

I have checked the rear Sam it appears to be dry, No water in that location.

Thank you both I will have to find someone with a star diagnostic as the one I have only contains four options on the tool.

 

[joderest]

have to ask, have you had the vehicle long ?
Only asking because i have the older ML270, if i fill it right up, i can go about 120 miles before gauge moves, then it quickly goes down to half a tank, then goes down slowly before needs fuel again.
If it was working ok and you have owned for a while, then you may have a fault. Try doing a few more miles then re fill it, may be the float has got stuck ?

 

[matt123]

I have had it for a while now.
It all began when the electronics on the car began to play up. I checked the battery terminals and realised the negative terminal was very loose so I tightened it and have it a full charge.
I then filled up a full tank of fuel and after doing some mileage noticed the gauge was only moving 2cm back and forward.
It may be the float do you know without opening it I can reset it.

 

[DREAMER NO2]

Dont know if this will work on new Mercedes, but i used a bottle of Red X in my tank after i took the car out of winter wrap up .I found the fuel pointer on fuel gauge was erratic and in some places not moving at all . This sorted it out for my pointer .

 

[M80]

I would see what's happening after 200 miles.
You can get a lot more miles before running out so wouldn't be too concerned, yet.

After thought. It's that time of year when winter additives are added to diesel. Is it possible it has been over dose with summat that is causing some foaming in the tank?

 

[alexanderfoti]

I would say potentially the rear SAM is damaged from the loose battery connection.

You need to measure the resistance of the sender wires going into the rear SAM to determine if the SAM is faulty, or the sender is faulty.

 

[DREAMER NO2]

Dont use Red X if it is not safe to do so on the bottle, i find diesel mentioned now please say to start with it is just guess work with some profiles .

 

[matt123]

Mine is a petrol ml350 I have done another week and the fuel gauge has decreased but ever so slightly.

 

[matt123]

I would say potentially the rear SAM is damaged from the loose battery connection.

You need to measure the resistance of the sender wires going into the rear SAM to determine if the SAM is faulty, or the sender is faulty.

If the SAM is faulty wouldn’t it throw of other errors in the car?

 

[matt123]

Dont know if this will work on new Mercedes, but i used a bottle of Red X in my tank after i took the car out of winter wrap up .I found the fuel pointer on fuel gauge was erratic and in some places not moving at all . This sorted it out for my pointer .

I wonder what it would have fixed by adding an additive.

 

[DREAMER NO2]

I did it worked for me .

 

[Simon22]

Had a rear sam fitted to my ML 2 weeks ago, my fuel gauge wasnt reading at all, i also had other electrical problems with the car, the sam looked fine from the outside, took all the connections of the sam and they were all corroded

 

[alexanderfoti]

If the SAM is faulty wouldn’t it throw of other errors in the car?

Not always.

 

[mattkh]

I wonder what it would have fixed by adding an additive.

Lubricated/cleaned the float mechanism.

 

[matt123]

Had a rear sam fitted to my ML 2 weeks ago, my fuel gauge wasnt reading at all, i also had other electrical problems with the car, the sam looked fine from the outside, took all the connections of the sam and they were all corroded

with yours you mentioned other electrical issues. I had that problem but that was due to the negative on the battery being loose. Mine seems to be just the fuel gauge.

 

[matt123]

Lubricated/cleaned the float mechanism.

I don’t know how that would work.

The dial has gone down to half now which means it’s moving but incorrectly.

 

[matt123]

Not always.

The fuel gauge has gone down to half way now. I will have to see if it goes down normally from there on.