Hey Scotty, gotta 2000 Mercedes SLK230 with 178,000 miles. I noticed the past few weeks the fuel gauge ready slightly below full after filling up. Could the fuel level sensor or fuel pump cause this? I don't have any warning lights on the dash.
If your odometer still works, just fill it up every 200 or 300 miles. I have a 1999 Ranger whose gas indicator is wishy washy. Every 270 miles is a mandatory fill-up. It leaves me with approximately a quarter tank.
S.O.P. for the many cars I've had over the years with hinky fuel gauges!
Save time messing with sending units, haha. After 23 years, you pretty much know it's the sending unit in a Mercedes. While I was having the brain bleed, I tried to stop for gas, but I was too confused. I started my truck back up, went home to get my girlfriend to take me to the hospital. It tripped the light shortly afterwards.
Welcome to the world of Mercedes fuel level sensors. My 2003 e320 had the same problem. First time the left level sensor went bad, I ended up replacing the right fuel pump and left filter assembly. That fixed the issue. Short time later it started doing it again, this time it was a loose harness at the rear gateway. Simply plugged it back in and problem solved. 6 months later my right level sensor went bad and ended up sending the fuel pump assembly back under warranty. Two months later my guage was way off. I drove till I had just under a 1/8th of tank and filled up. I did that to recalibrate everything and luckily that worked. So far it's been working properly, unfortunately this is extremely common issue.
Yours may just need to be recalibrated as well. Wait for gas light to come on or just before and fill the tank. Alot of times the level sticks or loses its calibration and filling up when almost empty does fix it on occasion.
The level sensor maybe failing or you have a loose connection. If the connection at the gateway is faulty you will usually have other issues such as no chimes going off when lights are left on when car is turned off, some cars the courtesy lights in door won't work. Same goes if you shut off car open door and leave key in ignition. This may not apply to your car, so this isn't a guaranteed way to diagnose it. I would have to look everything up later for you when I have my laptop.
If you have a scan tool that has full system/module capability that will help
If you scan the car and the level sensor code( if you have one) is showing up in the rear sam / gateway/ communications module you know the sensor is probably bad. If the code is showing up in different random parts of car you have a loose connection at one of those points
Try filling up first and use Chevron techron fully system cleaner. You may have some build up on the sensor. You can run it at double strength. Just don't use more then that , it is a waste as that is the useful max.
Thanks for the all the tips above guys. I am assuming it is the fuel level sensor getting old and just sticking. Actually, I did notice the next time I started my car, the fuel level sensor was reading normally. It seems to be happening on and off, and the reading is ever so slightly off.
I also do keep track of my fuel using the mileage counter ever since I bought my car. I reset my mileage counter whenever I fill up. My car gets around 260-300 miles combination of city and freeway driving. I usually fill up around the 280 mark. On the interstate it is about 320-340 before filling up.
So far the gauge is reading correctly I'd say 90% of the time, so I'll just have to be ready to fix this issue once it starts to get worse. I will probably do a fuel filter and fuel pump replacement while I am at it, since I think my car is still on those original parts as well. I will also check the wiring because I didn't think of that too.
In fact, another family of mine has a 1998 CLK320 with over 210,000 miles. Lately the fuel gauge wouldn't even read some days, and some days it worked fine. It would just stay below the empty line. I was confused why this was because the fuel level sensor was just changed recently, perhaps the wiring on that could be faulty as well.
https://www.pelicanparts.com/techarticles/Mercedes-SLK230/23-FUEL-Fuel_Level_Sender_Replacement/23-FUEL-Fuel_Level_Sender_Replacement.htm i misread the year I thought it said 2003 so you don't have a level sensor on each side of tank with the fuel filter being in tank. It doesn't change anything tho. It's either the level sensor, rear sam, gateway if available or wiring. It's almost guaranteed its the level sensor, as stated before the part does fail and when replaced seem to fail at higher rates if they even work at all. The cars might be pain but the way it was designed there are only a few possibilities which makes it very easy to diagnose. Update us when fixed
Test the fuel level sending unit and check wiring.
