In the past I have always reset the OBC after each fill up and compared the mpg to my manual computation.

To arrive at a gallons of fuel used: I have attempted to fill the tank to the same level each time by 1)filling up at the same station 2) same pump 3) fill until the pump clicks off then add more slowly until it clicks of again.

I have now discovered a better way.

I can now access the Fuel Tank Digital Information that is stored in the ECU and determine how much fuel I have used at any time, not just at fill up. I have only experimented with this the last two days and need more milage and fuel usage to then do a comparison to the OBC numbers. The OBC and my manual calculations have always been close for a "full" tank but I am interested in how they will compare for shorter trips.

I have also discovered, I think, that the "reserve" fuel remaining after the red fuel gauge light comes on is 10.4 Liters or about 2.7 Gallons. I'm going to run down to the light and see if I can verify this before I fill up the next time.

 

How exactly are you accessing the Fuel Tank Digital information?

 

>>How exactly are you accessing the Fuel Tank Digital information?

You enter "Test Mode" in the odometer/Oil Service window of the speedometer.

To do this:
1) Hold down the trip button until you see 1 -- tESt
2) Release and then press the trip button again, again and again until you see 19 and a flashing L--on or L--off. Press the trip button once more while L--off is displayed.
3)Press and release the trip button a number of times once again to reach 6.0

Test 6.0 is the Fuel Tank test and shows the number of liters in the right/left tank (there are 2 sensors, a right and a left with a baffel in the tank - I think).
Example: 087128 means there is 8.7 Liters on the left and 12.8 Liters on the right
Test 6.1 is the total fuel in both tanks, right plus left may not equal total because of rounding(?) by .1 Liters.

NOTE:You need to remain still while sitting in the car and doing this, any motion will cause the numbers in the test to change up and down as the fuel "sloshes" around
in the tank.

An update on my experimenting:
So far I have only driven 10.5 miles and used 1.7 Liters of gas as measured using this method. This computes to a MPG of 23.4 and the OBC is showing 23.5 after being reset to begin the experiment. Very small gas usage but the OBC seems to be right on, I'm pleased with the results so far. My guess that the reserve gas after the light comes on is 10.4 Liters is now even more of a guess; I'll know when it happens.

 

a Mini hacker ...

 

Wow did you figure that out from trial and error or have something to go with?

Too much time on your hands?

 

>>Wow did you figure that out from trial and error or have something to go with?
>>
>>Too much time on your hands?

Too much time - probably.

Figure it out - no way. There is a thread on MINI2 that gives the access information and what some of the Test mean but there is more data that is unknown than known.

The MINI Tests should also be similar to BMW and they are with one glaring exception and that is Test 20 for BMW which I can't find on MINI. This is for the Fuel Consumption Factor which I think is the "key" to the 'S' OBC reading 10% high while Cooper OBCs seem to be very close.

 

I have a BMW reset tool but that is about the most advanced diagnostic tool I have specificly for BMW's.

I have a Tech II OBDII diagonstic code reader too so that should work on a MINI.

Neither of those will tell you anything about fuel left in the tank though.

 

I filled up today after the low fuel light came on. There was 7.6 Liters (2 Gal) remaining at the warning. Using my normal fill routine the tank was "full" with 48 Liters (12.7 Gal). Therefore, if the capacity is 50 Liters and a different pump does not click off as quickly I could have put in another 2 Liters (.5 Gal) or a 4% difference. Partial fill ups could result in even larger % differences.

The question of how "full" is "full" has bothered me in the past, but I can now determine usage without that possible error.