Fuel Level Sensor not Working

[Pat Pickens]

Just when I thought my 24K mi. self-service was done and I had not screwed the pooch...

After re-installing the gas tank on a 2007 GS, which I have done a number of times, the fuel level gauge is not working. There is a low fuel warning. The connector at the left hand fuel pump looks ok. The contacts were cleaned and the connector reseated. Resetting the electronics by removing the battery leades, reconnecting and twisting the throttle twice did not help.

I do not know how to troubleshoot this one.

What do you think?
- could this be a CANBUS issue and it needs to rediscover the fuel level sensor?
- maybe recalibrating the level sensor is needed?
- could one the plug wires have gotten disconnected inside the plug?
- Anyone ever replaced a harness plug? Source for replacement plugs?

I'll try anything before I give up and take it to the dealership. No ding on them except nothing they do is cheap!

Thanks,

[marc]

Fuel sensors on bikes with the onboard computer are known to fail. Often. Some folks are on their 3rd and 4th sensor. Normally I'd assume that is the issue except that it happened right after you removed/installed the tank.

If your bike doesn't have the onboard computer option you may have a float version of the sensor. If that is the case perhaps your float got stuck.

One think you can rule out is the CAN-bus. The ONLY things connected to the CAN-bus are the instrument cluster, ABS controller, Engine Management Controller, Central Chassis controller, and alarm or alarm/TPM if you have those options. The fuel tank sensor is directly connected to the ZFE (Central Chassis Controller).

[Pat Pickens]

Thanks Marc. Ruling things out is a good start and farther than I had gotten. I have an onboard information display. I agree that despite those level sensors failing, it is too much coincidence that this failure happened with the tank being removed/installed. Maybe I will track down where the sensor connects to the ZFE and check that connection.

[marc]

There are two electrical connections at the upper left of the tank. One is for the fuel pump (three wires) the other is for the fuel sensor (two wires). I think. My wiring diagram may not cover the "with trip computer" model.



The connector on the right is the fuel lever sensor on my bike without the onboard computer.

[Pat Pickens]

The plugs are setup the same on my GS with computer except the fuel level sensor plug has four wires. I thought about removing the pump/level unit from the tank for more testing but that takes a special BMW tool to remove the silver ring. My money is on the level sensore plug having a bad wire but I am not sure how to test that or replace the plug. I can always learn to live with the warning light and set the trip meter each fill-up but not ready to go there yet!

[marc]

The metal cap screws on. I'd build a pin wrench from some scrap wood and screws. It beats paying $80+ for the fancy ring wrench.

[pdxrmccgs]

Does anybody know what years have fuel floats and what years have
fuel strips?

[marc]

I don't think it is a year thing, it's an options thing. If you have the onboard computer (OBC option) you have a fuel strip. It kind of turned into a year thing as most folks with 2007 or later bikes have the OBC option.

[pdxrmccgs]

Thanks..makes sense. What about the "embedded" computer chip
that is referenced as being part of the fuel pump/gauge system
on some of the electrical diagrams. Some electrical diagrams
show it feeding to the ZFE re the canbus. In other words it is
one of the few seperate nodes that is exterior to the ZFE
can-bus software or rather the can-bus software contained on the
ZFE chip or chips.

In other words prior to OBC you had a variable analog current indicating
the amount of fuel in the tank and for later models your information
is a node on the can-bus system running to the ZFE and this
node (or chip) on/or in the fuel tank has its own A/D converter etc.

If this is true where is the dam chip.

Rantings on fuel sensor strip: http://www.i-bmw.com/showthread.php?t=30198