[QUIKDZL]

This was my first post about a year ago, and as a noob, I didn't know how to post it without hijacking another thread. This information was valuable to me, so I thought I'd post it again properly. Maybe it'll help someone else. When I got my car, it was consistently reporting economy about 6.5% lower than actual, and this is how I fixed it. You can adjust what I call the on-board Mileage Correction Factor yourself using the BC Hidden Menus.

There are posts detailing all the menus, but the vast majority of it does not apply to our goal of adjusting the MCF, so I’ll simply give instructions for that.
• Car off, key out.
• Press and hold the trip odometer reset button (button) on the instrument panel.
• While holding said button depressed, insert keyfob into its slot, and then release button.

The display on your instrument panel where it normally displays the time, temperature, and miles accumulated (BMW calls this the BC) will display data in XX.YY format at the top and information below. The top line will read 01.00 indicating menu 1, submenu 0. The data below will read FGSTNR, German for vehicle chassis number. Below that on the bottom line will be the last seven digits of your VIN.
• Sum the last five digits of this number and write down the result. For example, if the number is XX24679, the correct sum is 2+4+6+7+9=28. This is your car’s unlock code.

Until you unlock the BC, only menus 01, 02, and 19 are available. We need to access menu 20. Pressing the button repeatedly will cycle between menus 02, 19, 01, etc.
• Press the button until BC displays menu 19.
• Pause for two seconds, BC will read 19.00
• Press button repeatedly until your lock code (28 in our example) is displayed after CODE.
• BC will display LOCK: OFF
• Press button until menu 20 is displayed.
• Pause for two seconds, BC will read KORR-VERBR, German for correction factor.
• Note the number displayed, and write it down.

This correction factor is based upon the European convention of fuel economy, litres per 100 kilometers (1 l/100km being equal to 235.6 mpg). Trust me if the math confuses you, but in Europe you would increase the MCF to get the car to display higher economy (consumption) numbers (using the reciprocal of our calculation); whereas in the US we would lower the MCF to get higher mpg numbers reported by the car. This is where you will want to use a calculator.

You should know what consumption your BC indicates (available by pressing the button on the end of the turn signal stalk), and you should know what your consumption actually is (manual calculations or a spreadsheet). Better yet, you may have been keeping up with this over several tankfulls and have average indicated consumption and average actual consumption. Either way, divide indicated consumption by actual consumption and multiply by 1000. For example, 32.5 Indicated / 34.5 Actual x 1000 = 942. This number is a good starting point for your “zeroing in” the MCF for your car. An even better number would be Indicated / Actual x Existing MCF. In this example 32.5/34.5=.942 would be the number you would multiply the existing MCF by to arrive at a new, more accurate MCF. Now that you know what you want your new MCF to be,
• Press the button to change the “ones” digit. It is already scrolling from 0 through 9. When it gets to the digit you want, press the button.
• Now the “tens” digit is scrolling. Press the button to select the digit of your choice.
• Now the “hundreds” digit(s) are scrolling (if I remember correctly, from 8-12). Press the button to select the digit(s) of your choice.
• The BC will have reverted back to menu 20.00 and is displaying your new MCF.
• To leave the BC menus, press and hold the button for 10 seconds, or remove the keyfob.

You’ll be amazed at how accurate your consumption readings will now be. They will fluctuate as fuel quality fluctuates, and if your driving habits suddenly change (highway/city ratio). Tweak as often as you like.

I've maintained a spreadsheet since I bought the car. The MCF was 1018 originally and over 18 tankfulls, the car reported mileage on average 6.5% lower than actual. After tweaking the MCF several times, I settled on 930. Now, over the last 32 tankfulls, the reported mileage averages 0.91% higher than actual (my goal was to be accurate within 1%). Driving style and fuel quality seem to be what cause fluctuations. At this latest setting, the lowest report from the car was 3% lower than actual and the highest was 5.69% higher than actual. The rare occasions where the report is more than 2% high are when my economy is unusually low (for me), such as when I did a little towing or no highway driving on that tank.

[Persian Whisperjet]

Quikdzl thanks that is super helpful. Mine too is consistently about 5-6 percent pessimistic, although oddly it is closer to accurate since I visited Jarek.

[QUIKDZL]

That's what prompted me to find this post. I am planning a visit to Bob in two weeks, and I figured I'll need to tweak the MCF again.

[BB_cuda]

Thanks Quikdzl. I access the same hidden menus but after unlocking using menu 19, mostly access menu 7. It shows the engine coolant temp in °C. I had forgotten how many of the last digits to sum. So, thanks for the reminder that it is last 5 digits. I normally drive local so I'm not in a position to get data for consistent usage on highway. My long trips (300+ miles) are only every 6 months to a year.

[QUIKDZL]

You're welcome! Trip distance doesn't matter--if your computer reports fuel mileage incorrectly, this is where to fix it.

[kbsilver]

My car also indicated MPG about 5% low. I did this correction, but when they updated the DDE program, the correction was wiped out.

[QUIKDZL]

You should be able to go back in and correct it again, right?

[kbsilver]

Originally Posted by QUIKDZL

You should be able to go back in and correct it again, right?

Yes I could, but figured another update will come along and clear it out again. I just add the 5% to the indicator in my head.

[digitaldav]

So how do we know if our odometers are reading correctly. Doesn't the mpg calculations based on the vehicles odometer? Most all speedometers are 2-4 mph higher than actual. Will this not effect calculations?

[QUIKDZL]

If the OD of your rear tires is stock, your odometer will be right. The speedometer correction built in by BMW (-3 mph) does not affect the odometer.

[Nadir Point]

Originally Posted by QUIKDZL

The speedometer correction built in by BMW (-3 mph) does not affect the odometer.

First I've heard that - what's the deal? My car reads ~4mph high.

[QUIKDZL]

Originally Posted by UberArchetype

First I've heard that - what's the deal? My car reads ~4mph high.

I would assume that your tire diameter is less than the BMW-designed diameter of 24.9 inches. At this diameter, each revolution of the tire moves the car about 80 inches. Since the final drive ratio is 2.81:1 and top gear is 0.69:1, for every engine revolution in top gear, the car moves about 41.26 inches. At 2000 rpm, this becomes 82,521 in/minute, or 78.15 mph.

Working the numbers backwards for a 4 mph difference, I suspect your tires are about 24.1 inches in diameter. Any chance you are running 225/40-17s instead of the OEM 225/45-17s?

[logandeere]

To my understand and correct me if I'm wrong but Bmw does this slight increase in the miles for legal reasons in different countries this is purposely done by Bmw
http://www.e90post.com/forums/showthread.php?t=459423

[QUIKDZL]

That's my understanding, too. I've read a bunch about it and my memory is that it stems from a European regulation that places a heavy fine on a manufacturer if the speedometer reads faster than the true speed. So BMW designed their speedometer to display a "corrected" value. They apparently chose to display 3 mph lower than true speed.

You can enable a digital velocity display on your BC (right there along with range to empty, mpg, etc.), and choose to display the actual velocity or the corrected velocity. Corrected velocity always agrees exactly with my speedometer, and uncorrected is consistently about 3 mph lower. Since it displays a whole number without a decimal place, it rounds the number so I have occasionally seen a difference of 2 or 4 mph from the cruise control setting as I went up and down hills.

Your trip computer (if you have Nav) will confirm this. Set your cruise control at 70 on the highway and then reset the trip computer. Your average speed will automagically report 67.

[logandeere]

Originally Posted by QUIKDZL

That's my understanding, too. I've read a bunch about it and my memory is that it stems from a European regulation that places a heavy fine on a manufacturer if the speedometer reads faster than the true speed. So BMW designed their speedometer to display a "corrected" value. They apparently chose to display 3 mph lower than true speed.

You can enable a digital velocity display on your BC (right there along with range to empty, mpg, etc.), and choose to display the actual velocity or the corrected velocity. Corrected velocity always agrees exactly with my speedometer, and uncorrected is consistently about 3 mph lower. Since it displays a whole number without a decimal place, it rounds the number so I have occasionally seen a difference of 2 or 4 mph from the cruise control setting as I went up and down hills.

Your trip computer (if you have Nav) will confirm this. Set your cruise control at 70 on the highway and then reset the trip computer. Your average speed will automagically report 67.

I never thought about that so your Mac displays the true speed on average of the trip?

[Nadir Point]

Originally Posted by QUIKDZL

I would assume that your tire diameter is less than the BMW-designed diameter of 24.9 inches.

No, stock-size tires. 4mph high reading at 70mph, GPS-verified. I assumed it was purposeful by BMW after they told me they could not adjust it with an ECU poke. At least now I know why. The last set of summer tires I got for it are a tad bigger, which cuts the error in half.

[QUIKDZL]

Originally Posted by logandeere

I never thought about that so your Mac displays the true speed on average of the trip?

Mine does.

[QUIKDZL]

Originally Posted by UberArchetype

No, stock-size tires. 4mph high reading at 70mph, GPS-verified. I assumed it was purposeful by BMW after they told me they could not adjust it with an ECU poke. At least now I know why. The last set of summer tires I got for it are a tad bigger, which cuts the error in half.

Maybe electronic tolerances have aligned to give your car a larger offset than designed, but also be aware that the diameter (circumference) of a given tire size varies considerably from manufacturer to manufacturer. This is on display on Tire Rack's website. They list each tire's actual diameter (or they did last time I looked).

[dmanb2b]

Sorry to revive old thread, but anyone else run into this discrepancy? I just recently picked up my D and have been noticing a bunch of folks passing me or tailgaiting, yet I tend to not be the slowest guy on the road…if you know what I mean :>). (I figured maybe people really dislike BMW drivers...LOL). So flipped on my waze app and sure enough with cruise set at 80mph, waze indicated 72-73mph. Then set it at 90mph and sure enough waze reporting 81mph. I’m running bridgestone driveguard rfts in 225/45R17 all around. Tire rack has diameter listed at 25" and all four tires have at least 8/32nds. Just seems like a big variance to me...I could live with 3mph.

I’m guessing there is no way to adjust this discrepancy, other than having digital uncorrected speed read out on screen ?

[RollingCoal]

Originally Posted by Persian Whisperjet

Quikdzl thanks that is super helpful. Mine too is consistently about 5-6 percent pessimistic, although oddly it is closer to accurate since I visited Jarek.

Nice Info Quickdzl

Mine was the same until I got the JR Tune. Now it is extremely close to hand calculations.

[nicklockard]

Kudos. 5 star thread info.