R1150GS Fuel Gauge Repair

How To Fix A Sticking Fuel Gauge

About 8 months ago my ’03 1150 GSA did stop to show the top fuel bar on the RID even if filled up to the neck.
I did not pay much attention because after about 80mls the fuel gauge worked normal again.
Looking through some of the older threads on ADV I read that other members had similar problems but no conclusive solutions.
Cleaning the sensor potentiometer from residue as posted by MikeO did sound most promising and I made a mental note to try that next time my tank is off.
Last week my fuel gauge stopped working altogether and also my oil temp was sort of flickering up and down by one bar, something it never did before.
So it was time to get to the base of the problems since a new fuel gauge is 260.- (yeiks).

The flickering oil temp was solved quickly. The connector for the RID which is located under the tank (8pin plug in the middle, lower bank) did show visible corrosion on the positive supply pin.
Contact cleaner solved this problem as I posted in another thread. The fuel gauge still did not work.
Stocking up on a new fuel filter (was about time) and a new O-ring I started to take the fuel support plate off.
Before doing so, I measured the resistance of the fuel gauge at the connector for the fuel pump on the right side with a DVM.
The fuel gauge signal is the yellow cable measured against the brown cable (ground), the low-gas signal is the white cable measured against ground as well.

Low gas worked alright, it shows 0 Ohm if active and is open if enough fuel is present.
The fuel gauge did show an open connection which did seem wrong.
Next I removed the complete pump assembly and connected the DVM to the fuel gauge plugs of the tank-connector (yellow-brown) to monitor the resistance.

First I cleaned the potentiometer with a Q-tip, this had no effect.
Touching the wire rod which holds the float by accident I suddenly measured a resistance.
Basically pressing the wire down brought the fuel gauge back to life. Inspecting the potentiometer setup it was clear that the float arm had too much clearance
(moving up and down) at the pivoting mount which lifted the slider off the potentiometer. This does not affect the low gas slider which is closer to the mount.

So looking for a way to tighten the clearance of the mount I looked at the back of the potentiometer to discover the cheapest way of a bearing for the wire rod:
just a punch hole in a L-shaped metal sheet bracket which is part of the assembly. Not even a plastic bearing, el cheapo to the power of 10!!
Pretty clear that over time this hole will increase in size due to abrasion of the metal rod in the bracket thus causing
increasing play of the assembly. Basically sooner or later the missing first fuel gauge bar will occur just due to wear.

Bending the L-shaped bracket to the left decreases the free clearance (see picture) of the metal rod and keeps the fuel gauge slider on the potentiometer all time.
Problem of the dead fuel gauge was solved.

But wait a moment! I measured different resistance at full-gas position depending on the clearance of the metal rod!
So bending the metal L-shaped bracket needs to be done in an exact amount to assure that the first bar will show again.
This requires to determine the resistance which would entice the RID to show all bars.
The resistance of the fuel gauge potentiometer at full-gas position of the float was between 5 Ohm and 7.8 Ohm depending on the clearance of the rod, i.e. how
much one bends the L-shaped bracket.
Completely not content in testing the right resistance with mounting and un-mounting the tank a couple of times I recruited a precision potentiometer and
connected it to the RID inputs (yellow-brown) of the bike (connector on the right side, for the tank assembly), simulating a connected fuel gauge.
The results

To show all bars : resistance must be < 6.5 Ohm
The first bar doesn’t show: > 7.2 Ohm (which means if the clearance of the metal rod gets to high the first bar does not show, bend the bracket more!!)
All bars do not show: > 67 Ohm (at this position the low gas signal comes on as well)

Changes of the resistance do not show immediately on the RID though, there is an electronic dampening unit under the tank which delays changes (integrates the signal) to prevent rapid display changes during riding. Just wait 5 sec for changes to show on the RID.

Finally I adjusted the gap of the bracket to a 5.5 Ohm at the top position of the float and assembled the complete unit and put everything back in place.
Voila, fuel gauge works again, the top bar shows again, problem solved.
I hope this helps other 1150GSA riders. Does not apply to the 1200GS unfortunately.