Low Fuel Light comes on early now
 

Didn't have this problem for the first 6k miles of ownership.

It started happening when it was time for a new fuel filter, fuel pump, fuel pressure sensor, fuel module, and fuel module cable, (due to age and cracked LPFP cover) which cleared up a P008A CEL, but still the math ain't mathing.

Mostly city driving this tank. 17.4 gallon tank, so I should have 3.5 gallons left at 21.8 mpg for 304 miles. Should have 75 miles of range am I right? Or is range not factoring driving till the last sip? Not that I would ever run it dry. Usually let it get under 1/4 tank then fill at Costco with premium, and the light USE TO come on when the needle was just a tick above empty.

Why's it fibbing? 🤔

https://cimg3.ibsrv.net/gimg/www.mbw...59f1e70fa7.jpg
https://cimg4.ibsrv.net/gimg/www.mbw...b758e65f69.jpg

We are retired, so never concerned about MPG, so can't compare. Plus no idea about your model.

You should identify your vehicle - your profile shows, "Vehicle(s) I drive: Rental" ... so zero details. Also, you never stated current mileage.

We fill just before 1/4 tank, so no future stress.

I figured my name and where I'm posting would give it away, but it's a GLK 350, 2013. I sure hope retirement doesn't keep me from monitoring how my fuel system is working. I knew to look at my injectors for a drop in MPG before the car knew to tell me anything. One was coated in oil due to a failed injector seal. The m276 is the original "be a man" and often won't tell you it's hurting soon as it should. But I don't think any of this has anything to do with why my gas light started coming on at 1/8 of a tank.

Perhaps you're looking at it the wrong way; perhaps it's now actually showing you the correct level in the tank whereas the previously failing part(s) were skewing what the fuel gauge shows.

Well that's an interesting take, but it doesn't quite line up with the timeline of events. Before the new parts were put in this started happening, and hasn't corrected itself even though no more check engine light.

I don't know how anyone look at those photos and thinks that's right.

That's not a problem - that's a feature. I think one of two (maybe three) things are happening...

1) You didn't say you reset the counter when you last filled up, but I assume you did...
2) The "miles remaining" are calculated dynamically, based on some algorithm that heavily weights the calculations to the most recent driving you're doing. So if you average 25MPG driving 300 miles on the interstate to New York City and have two gallons of gas, you do NOT want the computer to suggest you can dodge pedestrians, food delivery kamikazes on e-bikes, and maniacal taxi drivers for fifty more miles.
3) I'm sure that MB (and from what I've seen, pretty much everyone else) build in a fudge factor. You don't get mad if your car tells you you have ten miles left if you figure out you really have 30 (OK, maybe you do...) but most folks DO get mad if it tells you you can drive 10 miles and you flame out in 6.

I don't think any of that explains the change. It never use to do this, and it's not normal for the gas light to come on with 15% of the tank still full.

I don't think you have 15% of a tank remaining. I've never had a car that would coast to a stop when the miles remaining hit zero (and I've done that many times, trust me).

Your needle is showing just a hair over 10%, and mid-30s miles remaining seems like a perfectly sensible point to warn the driver about low gas. I do drives where the next gas station can be 70-100 miles away.

Anyway, your description seems pretty much in line with what my car does as well.

I think the thing to do is to see how much gas it really takes to fill up your tank, and then do your calculations. Trying to discern how much fuel remains by relying on the miles remaining calculation is not going to be a good method. That figure can go up or down by nearly 50% based on the last few miles driven. Heck, according to the miles remaining, my car has gone 30-40 miles making more gasoline at times!

Good points.

For the record wife says light came on yesterday, so I'm guessing 20 miles prior. I have an OBD scanner and I've been monitoring this occurrence of the low fuel light coming on at what bluedriver reads is 15% left in the tank, for 2 months now.

If this hadn't started a year after buying it and before any fuel system parts were replaced it wouldn't seem so damn early.

AI Google 🙄 says anywhere between 10 and 15% is normal, but it didn't used to.

Since when does a 13 Glk get 21.7 mph city ? Mine gets 17-18 . Your screen can show avg mpg for immediate , same day, or avg. reset it. You don’t get 21.7 if you drive all city

Well sticker is 19 MPG city, but it really does depend on the city. That was mostly City this tank, but I would say 40% beltway highway.

She's always gotten great gas mileage. I got 26.2 mpg on a 300 mile one way trip recently, and 24.2 coming home, so 25.2 average, 99% highway.

Almost 142,000 mi. Got a bunch of parts money into it since buying 8k ago. New VVTs and timing chain tensioners. PCV valve. Plugs. I do all the work, except for what I had to have a shop program fuel system wise.

I am wrong I didn’t look closely at your avg reading .

Without regards to math, fuel mileage calculations, and distance to empty, this is EXACTLY where my ‘15 GLK350 turned on the fuel warning for the first (and last) 155,000 miles. That fit my wife’s driving style perfectly. She would run it down to empty, then do 2 more errands.

Parts manufacturing tolerances?

I think quite a few owners, of any brand vehicle, give too much credit to some of these readings. These sensors and guages are not built to some NASA level of accuracy and repeatability.

That's where mine comes on as well.
Also when I was experimenting with E85 I pumped the tank to empty once the light came on and I got 2 gallons out of it.

Let my light come on once just to check it to see how much it had left. I have a 66 litre tank ( convert that to the various gallon sizes if you wish) and I drove around 10 KM and filled up with 60 litres of fuel. Can't remember how the range to empty was.

So if I had filled up immediately I may have used 59 litres of fuel so around 7 litres reserve or close to 2 gallons US.

Normally fill up before tank dips to 3/4

Range until empty can never be accurate because you may speed up, drive on a hill, rough road etc.

Just verified on my '13 GLK350 that the low fuel warning came on at precisely 1/8 tank.