Hi all- I've seen a bunch of past posts but haven't found the fix yet. When full my gauge reads "full". When empty (I ran it out on purpose) it reads about 2/3. When I bought the car the sender was corroded so i replaced it with the slk320 equivalent, about 200 ohms empty, 5 ohms full. Checked wiring per the shop manual, continuity good, no shorts or opens. Instrument cluster provides about .7v at the unplugged sender connector. So I replaced the instrument cluster- exactly the same result. With the fuel gauge inop, car won't complete OBD2 monitor tests (cat & evap)- so car won't pass N.Y.S. inspection. All because of a fuel gauge! Anyone with first-hand experience? Love trhe car, but... Any help greatly appreciated! Thanks, the Panman

 

So you replaced the sending unit that goes into the gas tank?

 

Thanks Driver, yes. With a couple gallons in the tank sender is at 155 ohms & gauge reads 3/4. Sender is from an R170 series Mercedes.

 

We just had a problem like this on my father's 2007 Dodge Caliber.
The Caliber's sending unit is also the fuel pump and filter and the whole assembly goes into the top of the fuel tank.
We were getting false readings after my father's mechanic had installed the new unit. We took it back and they turned the unit a little and it's been fine.
When they installed the new one it was hitting something in the tank, so the float wasn't moving correctly.
I don't know if the Crossfire has the same setup, but maybe the float is hitting something?

 

Sounds like you have done all the correct troubleshooting. So I'll detail what I have found and hope it will help: Mercedes part number for sending unit is 170 542 11 17 original, then came 170 542 13 17 and now replacement 170 542 15 17.
From the 2008 service manual empty should read 20 ohm and full is 270 ohm. Voltage measured at the tank/sensor connection is 0.7 volts, as you have found.
When checking shorts and grounds the connection at the instrument panel must also be disconnected. Skip a continuity test and check ohms directly to ground and to each wire as well as the two wires to one another.

It is a simple two wire connection, no splices, no other wires between the sensor and the alarm unit integral to the instrument cluster. It sounds like you have taken all the right steps. I know from experience when Mercedes replace an original part with a replacement part/number there is sometimes something missed in the process and the new replacement will not work like an original. M60A3driver gave good advice. I too have bent the arms on fuel tank level sending unites to make them work correctly. Good Luck!

 

Hi, maybe you could try a dry test - buy a 0 to 500 ohm potentiometer and connect it to the wire going to the sensor. You probably have to calibrate the potentiometer first - find where 20 and 270 ohms are, set it for say 270 ohms, connect it up and see what the instrument cluster reads - then dial it down to 20 ohms, if it reads correctly, then you know it's your sending unit.
-Jerry

 

Thanks Red, I did just that. Still hasn't resolved the problem, but I ran it out, added 7 gallons to put it at about 1/2 tank, soldered a 600 ohm pot in series with the sender & adjusted it to read 1/2 tank. 2 drive cycles later, all codes cleared (completed monitor tests). I still haven't figured out what's goin on, but if I can get the gauge to read "empty" when it's empty I'll be happy with that. When I get it working properly I will post the final result to share. I appreciate everyone who contributes to the forum!

 

What is the part number on the replacement sending unit you are using? I'm curious what " i replaced it with the slk320 equivalent " actually means.

 

zip thanks for your help. As you know, the oem sender is no longer available, but all mechanicals are shared with the SLK320, built on the R170 platform. Hard to read but looks like pn A170 562 1017. Next to that, pressure sender A001 118. Full it reads .5 ohms. Empty it shows 197 ohms. The resistance changes smoothly out of the tank. With the sender out of the tank (but hooked up) if I hold the float in the "full" position the gauge reads "full". If I let it swing down to the "empty" position, the gauge reads "3/4". If I unplug the sender, the gauge drops to "empty".

 

Empty is too high it should read 20 ohms. You simply may have a bad sending unit.

New units are available at MBpartsgiant.com new tank sending unit They are not cheap, or you can try ebay for a used one. Current MB part number is 170 542 15 17. Like I said above Mercedes looses something in the replacement parts from the originals; try another sending unit because the 197 ohms is way off. please read my post #5 and glean the info.

Trying to make a bad unit read correctly just isn't going to work. What you read at empty 197 ohms is not close to the 20 as specified in the service manual. see my post above #5.

Good Luck ~ Keeping these cars running is indeed becoming a challenge.