BMW E39 fuel gauge jumping around
E39 fuel gauge jumps around or sticks, what causes it?
The cause is usually the sender unit in the tank or its wiring, not the instrument cluster. A wire can be broken inside the insulation even though it looks intact from the outside. The float can also come off its arm, or the arm can jam because of dirt.
How do I tell an E39 fuel gauge fault from an instrument cluster fault?
The cluster test is done from the hidden service menu. If the fuel gauge rises to full in the test, the cluster works and the fault is probably in the tank sender or its wiring. The hidden menu also shows the level in each tank half separately.
Why is one half of the E39 tank full and the other less full?
The tank is in two parts. The right side is filled completely first, and fuel moves from right to left over the driveshaft tunnel. The left side is supposed to empty first, so the difference is normal.
Can a replaced instrument cluster cause fuel gauge faults?
Yes, if the coding of the replacement cluster does not match the car. Then the temperature and fuel gauges can read wrong. The same part number can fit different engines, so check which car the cluster came from.