Fuel Gauge is Tripping

[Avetiso]

Start my car, fuel gauge goes up to 1/2, where it should be. But it starts fluctuating up and down, and the miles-left readout on the cluster jumps plus/minus 20-30 miles and everything in between. Only happens after a start up and at idle. Once you start driving (like 15+ mph) it goes away. Happened to me before yesterday three times, but it hasn't happened since. Is my sensor dying, or do phantom things like this happen? If it is dying, which sensor is it?

[danewilson77]

The leveling system is built onto the pump I believe.

See that float. I believe that's where the signal for tank level indication comes from.

[derbo]

Sounds like one of the sensors is dying. My bet is the fuel pump side is dying cause its under 1/2 and its jumping around.

Normally the last half of the tank is by the right side (fuelpump side). The fuel tank usually will pump the fuel from the left side over to the right side as fuel tank goes down.



Have the car running.
1. Hold the left side gauge cluster knob until you see TEST on the dash.
2. Now press the knob till the menu number reaches 19. It should be ON.
3. wait till it says OFF and then press the knob again till you reach 6.0.

In the odometer area it should now show 6 digits showing your fuel levels from both sensors. The left 3 are for the left sensor and the right 3 are for the right sensor. If I remember correctly, the numbers are 270330 for a full tank. I know there is another option called 1_6.2 if you press the knob again.

1 = both sensors ok
2 = one sensor fault
3 = implausible input

the problem with 2_6.2 is that it wont tell you which one is it. I suspect its the fuel pump side one but there is a leveling sensor on the left side. I would do 6.0 test and make sure the fuel levels aren't jumping around. Since the readings are seperate you can see which side is jumping around if you have a full tank.

[Avetiso]

It wasn't "under" one half, it was right at it, and it was tipping into below and over. Could it be that the sensor was simply readjusting as fuel was being pumped between tanks?

Either way, I'll do this test when I am in my car again and will report back.

[derbo]

it shouldn't be visible moving back n forth dramatically like that. I had a similar problem and I had the problem over 1/2 a tank. I suspected it was my left sensor and GT1 confirmed it was faulting. I replaced that and ultimately the right side followed a few weeks later

[Avetiso]

Ok.

With the six digits:

Left three digits were alternating between 15-16.

Right three digits were reading between 190-192.

The code reads 1_6.2.

[derbo]

From my understanding and experience with my own car, the left side empties out to the right side when the right side goes low. The left side should be 0 when the right side is empty. I'm not 100% on what the numbers are suppose to be on the 6.0 on a full reading. Anyone have a full tank that can check?

The only other way I can think of, is to plug into a GT1 or ISSS to read the number of faults of the bmw level sensors.

[telijah]

I have an "almost" full tank I can try to check later...

[derbo]

So this morning when I drove to work it was max on the right. I took a hard right turn and the numbers went up on the left and down on the right. Once I started driving straight again the fuel started to pump back to the right to max out at 330.

This is the way I believe the fuel pump works. That 15-16 on your left side should be pumping into the right side.


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