Fuel gauge shows empty, but no warning light
 

Fuel gauge was acting a bit odd, in that I noticed over about 50 miles and several short drives that I would park the car with just below half a tank, and start the car with just above half a tank. Then, today, it suddenly dropped to empty... but the warning light is not on. Range shows ---.

Any suggestions on this?

Thanks,
Paul

It has something to do with fuel sensor. Just fill up your tank or put atleast $30-$40 worth of gas. Your gas gauge should work back to normal again. Well, that works on my w211 AMG and I do that everytime it happens.

Nope. Just filled up. First of all, it took over 20 gallons, so the 1/2 tank it was showing before it died was not correct. Now it's full, but still shows empty.

I do think you're right that it's the sender, though. If the gauge itself were bad, Range would probably work; and the way I've seen these German senders work is that reserve (where the light comes on) is a separate switch from the resistor that senses the level. If the resistor is broken or the wiper is not making contact, this seems like a likely result.

On the other hand, this could also be a problem wherever the sender level signal is converted and put onto the CAN bus. Anyone know where that happens? Is it at the rear SAM, or the middle gateway, or ...?

AllData says that the signal does go through the rear SAM. Probably not a coincidence. I wish I could find out which connector.

Also, the system indicates a malfunction by setting the gauge to empty but not illuminating the warning light. Still a question of whether the malfunction is in the sender or in the SAM. I'm now thinking SAM.

My 2009 has acted similarly. On a 500 mile day about 400 miles into the tank the gauge suddenly read empty and range was --. Finished the 500 miles. A few days later it was still reading empty and null range when I topped off the tank with about 18 gallons and suddenly had a working gauge.

In my case I think something is amiss with the sensor in the tank. Dealer wouldn't look at it under extended warranty because 1) its working now, and 2) no fault codes logged. Fine, my first and last Mercedes-Benz.

When it happens again I'll pull the rear seat and carpet up to get the sender out of the tank. Its as if a string or trash is somehow in the tank.

As far as I can tell, there are two senders (one on the left side, one on the right).

I finally found a wiring diagram that shows which wires and which pins carry the sensor signals to the rear SAM. I'm going to measure these with a meter tonight to see whether the problem looks like one of the senders or the SAM. If I can't make any progress from there, next step will probably be an independent shop I know.

Finally found the proper wiring information. Wires are BN/BK (common), BU/BK B4/1 (left sender) and GN/BK B4/2 (right sender).

With a nearly-full tank I am reading 270 Ohms for the left sender and 115 Ohms for the right sender. Both of the values move up and down when I rock the vehicle to makes some waves in the tank.

Which reading is right? Which sender is bad?

After using a bit more than half a tank, I am now reading 463 Ohms for the left sender, and 370 Ohms for the right sender. So the two senders are tracking pretty closely, but there's about 100 Ohms extra resistance on the left. I would guess this means the left is bad...?

Also, both times when I made the measurements, the right side of the vehicle was a little higher, which should make the fuel level on the left higher, and the resistance on the left lower, but it's reading higher. More evidence that the left is bad?

The information I had was incorrect, or I read it incorrectly. The left sender is GN/BK, the right sender is BU/BK. I finally got access to my left sender and I find there's nothing wrong with it!

BTW, with the float arm raised fully, the old and new left side senders both read in the 100 to 110 Ohm range.

I removed the BU/BK wire at the connector at the SAM and connected both pins to the GN/BK wire. Now my gauge works. Seems like a solution, at least for the short term.

Can you please email me a copy of the wiring diagram so I can do this fix as well. TY

JONOTEGA@GMAIL.COM

Here is a copy of the wiring diag. at the rear SAM. Note the position of wire #40 Grn/Blk and wire #27 Blu/Blk.

The conn. view is the back side of the conn. so make absolutely sure you are connecting the two wires on the top side.

https://cimg0.ibsrv.net/gimg/www.mbw...83aedfbc7e.jpg

This post is somewhat old and I don't know whether anybody still reads it. Since I encountered the same problem a little while ago I only now came across this thread. I tried to locate the wires you are referring to but don't really know where they are. Can you point them out on the picture below. I want to try your solution. The MB workshop manual says you need to update the SCN, which of course I can't.

I accidentally posted my query below but it supposed to go here.

KJ, explain what your problem is and make it short.

What model ML do you have?

ML280CDI W164 2006 German model.
The fuel gauge shows empty but the empty warning light goes out once the engine was started. See post further up. I am not sure which wires to connect where. Are all on connector C or do I have to move some over from another connector?

Your problem is the reverse of the original poster. Please get a scanner that will read codes in all modules.

However, the workshop manual describes this exact problem, which I read as the same as the OP's. That's why I thought that changing the wires as per above would do the trick. I had it checked for error in all modules. Stangely enough. the gauge did not come up.
My model is technically identical to the one below.
Thanks.

Quote from manual
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ML 350 4MATIC (164.186) V6-3.5L (272.967) (2006)

Instrument Panel, Gauges and Warning Indicators > Fuel Gauge > Component Information > Technical Service Bulletins > All Technical Service Bulletins: > T-47_00-41 > Sep > 06 > Instruments - Fuel Gauge Drops To 'EMPTY'

Fuel Gauge: All Technical Service Bulletins
Instruments - Fuel Gauge Drops To 'EMPTY'

Date: September 27, 2006
Order No.: T-B-47.00/41
Supersedes:
Group: 47

SUBJECT:
Model 164.175/186, Up to VIN A088895

Model 164.871, Up to VIN A077783

Model 251.165/175, Up to VIN A017709

Fuel Gauge Reads Empty

If you receive customer reports in the above model vehicles of the fuel gauge dropping to empty with no activation of the reserve light and the below
symptoms, this may be resolved by updating the instrument cluster fuel parameters per the below procedure.

-

No faulty fuel pump found in the fuel system

-

No obstructions found in the fuel tank

-

Includes fault code 9135 "Fuel tank sensor tight recognition: The signal from the fuel tank sensor 2 is not plausible" in the instrument cluster

To update fuel parameters, SCN code the instrument cluster per DTB T-B-54.30/136d, "Instrument Cluster SCN Coding for Component Replacement or
Dealer Installed Accessories" or S-B-58.00/144a "On-Line SCN Coding Instructions for the STAR Diagnosis System".

Understand that there is no Check Eng. Light for problems in the Instrument Cluster. When there is a problem like yours, the codes must be read in all modules. If you do not have the correct scanner, everything is guesswork.

Notice that SCN Coding for Component Replacement is necessary, but you will not be able to correct the problem if you do not have the proper scanner or you will have M/B do the coding.

Hi guys after searching I have found this thread

may I please ask which wires are the two fuel sensor feed wires into the sam from each side

is it pin 27 and 40 on connector C??

and the one feed out from sam to the cluster ( fuel guage) ?

Did see the pics above couldn’t find any info on the feed out to cluster fuel guage
Thanks

Please UPDATE YOUR PROFILE to include the year and model (gas or diesel) and where you live. Without this info I cannot help you.


https://cimg0.ibsrv.net/gimg/www.mbw...6491e21088.jpg

Done


I have a 2006 280ml diesel

What don't you understand about the previous posts that I supplied?

Go to the rear SAM, locate conn. C and find the appropriate wires.
https://cimg4.ibsrv.net/gimg/www.mbw...3527c03daa.jpg
https://cimg5.ibsrv.net/gimg/www.mbw...48aa73cd8e.jpg

I can’t work out what is the wire that goes from sam to fuel guage

I understand the two in from senders and there position on plug