Fuel Level Gauge not working after fuel pump and sender replacement
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Joined: Feb 2010
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2001 c320
Fuel Level Gauge not working after fuel pump and sender replacement
I had my fuel filter replaced last week as long needed maintenance. The mechanic said my fuel pump had low pressure and eventually needed replacement for reliability. I decided to replace the fuel pump. After getting into the process of replacement, I discover the new fuel pump connections have been updated and will not connect to the old fuel sender(on the driver's side).......so I end up replacing the right fuel pump and the left fuel sender. After tightening up everything and starting the car, my fuel gauge will light up yellow right before the crank, but when the car is running the gauge reads empty....even the "miles left" indicator reads blank....just seems dead.
I know I correctly installed the pump and sender(and did not break the levelers!). The C320 drives nice.......I'm at a loss as what to do. I know I have about 4 gallons of gas(I pumped the gas out right before starting the work). I have not filled the tank(just the existing4 gallons) to see if that kick-starts the fuel gauge level.....I would hate to have to pull everything out with a full tank. The negative battery cable was disconnected during the work and reconnected at the end. Is there a step I am missing to get the fuel level gauge working again?!
I know I correctly installed the pump and sender(and did not break the levelers!). The C320 drives nice.......I'm at a loss as what to do. I know I have about 4 gallons of gas(I pumped the gas out right before starting the work). I have not filled the tank(just the existing4 gallons) to see if that kick-starts the fuel gauge level.....I would hate to have to pull everything out with a full tank. The negative battery cable was disconnected during the work and reconnected at the end. Is there a step I am missing to get the fuel level gauge working again?!
Last edited by du_man; Jul 3, 2015 at 10:39 PM.
Junior Member
Joined: Jul 2015
Posts: 26
Likes: 0
2003 C240
I've had the same problem for a while now. After I replaced my pump and sender my fuel gauge wasn't reading right. But after a fill up it started working until I get lower than a half tank then it would stop moving and eventually the car would shut off as if im out of gas. When that happened i decided to open the tank from both sides and I found out that the side with the sender is dry but the pump side is full. I've done some research on the problem but all I could find out is that both the pump and sender are supposed to balance each side out. But for some reason the sender is sending fuel but none is returning to that side. I also read the tubes could be hooked up wrong.
Hopefully we can get some more experienced members to help us out.
Hopefully we can get some more experienced members to help us out.
Junior Member
Joined: Mar 2017
Posts: 65
Likes: 12
1995 E420, 1998 E300TD, 2002 CL230K 6spd, 2002 CL230K auto, 2002 CL280T VR6 Project, 2001 A6 2.7T
There are two types of fuel level sensors that could be installed in the 203 chassis, the older style, 4 pin plug "resistor card" sensors up to aprox. 9/01, and the newer style, 5 pin plug "MAPPS" sensors as of aprox.10/01. If you retro-fit the MAPPS sensors to the older cars you have to re-version code the rear SAM and Instrument cluster for the MAPPS sensors. Some older cars have SAM modules and instrument clusters that can not be coded for this and would have to be replaced with newer versions to complete the retro-fit. Another problem occurs when just one side is mis-matched as the right side fsu of either type will "just plug in", inside the fuel tank, but this combination will never work the fuel gauge.
Hope this helps
Hope this helps
Last edited by junkyarddawg; Mar 31, 2017 at 09:55 PM.
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Joined: Mar 2004
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From: Boston, MA
'14 ML350, '13 C220 CDI, '07 C280, '98 ML320
Thanks for that info.
I replaced fuel pump and sender unit [as a preventive maintenance] about one and half year ago on my '07 C280. They worked fine for a year and the fuel gauge started to not show correct fuel level - after filling up the tank, for the first half [of tank] of usage, fuel gauge doesn't move at all (stays at full). Once half tank of fuel has been used up, the gauge starts to work and goes down to half mark when the tank is in fact empty.
I replaced the sender unit. Fuel gauge worked for couple of tanks of gas and went back to same problem.
I replaced fuel pump and sender unit [as a preventive maintenance] about one and half year ago on my '07 C280. They worked fine for a year and the fuel gauge started to not show correct fuel level - after filling up the tank, for the first half [of tank] of usage, fuel gauge doesn't move at all (stays at full). Once half tank of fuel has been used up, the gauge starts to work and goes down to half mark when the tank is in fact empty.
I replaced the sender unit. Fuel gauge worked for couple of tanks of gas and went back to same problem.
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Junior Member
Joined: Mar 2019
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Likes: 1
C230
I ran into this issue on a CL a few months back. Another tech had installed a new sender but it still had issues. Found the rear sam soaked in water. Replace the rear sam but the reading was wrong. Found the wrong NEW sender had been installed. Installed the correct sensor and now working correctly.
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Newbie
Joined: Jul 2021
Posts: 11
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C55 AMG, 2006 C55 AMG, CLS55 AMG
Im having same issue
I've had the same problem for a while now. After I replaced my pump and sender my fuel gauge wasn't reading right. But after a fill up it started working until I get lower than a half tank then it would stop moving and eventually the car would shut off as if im out of gas. When that happened i decided to open the tank from both sides and I found out that the side with the sender is dry but the pump side is full. I've done some research on the problem but all I could find out is that both the pump and sender are supposed to balance each side out. But for some reason the sender is sending fuel but none is returning to that side. I also read the tubes could be hooked up wrong.
Hopefully we can get some more experienced members to help us out.
Hopefully we can get some more experienced members to help us out.
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