My BMWs have always been spot on when it comes to brim-to-brim checks. But over the years I got quite a lot of complaints from customers, especially after the software update or even simple coding.
The last one, an N55-powered X3, on-board computer was so optimistic that even the maximum correction didn’t sort it out. The problem appeared after the instrument cluster retrofit. The customer noticed the overly optimistic range prediction after the first gas station visit.
I advised him to use a few full fuel tanks to see if there would be any changes.
Unfortunately, that hasn’t changed anything. Then I asked him to write down the exact mileage and the amount of fuel filled to the brim.
Armed with new data, we arranged an appointment and I tried to adjust the range indicator prediction with the ISTA application.
But, before we move forward, I’ll try to briefly explain how the system works.
How Does Range Prediction Work?
The DME/DDE (engine control unit) calculates the amount of fuel currently being consumed and sends the value to the onboard computer (OBC). Here the fuel consumption is calculated in l/100km or mpg and displayed in the central information display (iDrive) and/or instrument cluster.
How to adjust the fuel consumption indicator?
There are two ways to adjust the consumption indicator:
- Via BMW ISTA service function
- Via instrument cluster hidden menu
I’ll cover both procedures, but if you have access to the ISTA setup it’s easier and better.
Fuel Consumption Adjustment With ISTA
Prior to transfer to the onboard computer, the consumption signal is multiplied by a correction factor in the DME control unit. The correction factor is set at the factory to 1.0 and is adjustable within certain limits with the consumption calculation adjustment function.
Before starting the adjustment you’ll need to have the following values:
- Fuel consumption calculated by the on-board computer
- Real fuel consumption calculated on the basis of refueling
These two values must be entered during the adjustment procedure. The matching factor then automatically calculates the correct correction factor and transfers it into the DME control unit.
The correction factor can decrease or increase by max. 12%.
Determining Actual Fuel Consumption
- Refuel your car to full (to the brim)
- On-board computer: recalculate fuel consumption
- Drive the car for several hundred km/MLS
- Refuel to full again
- Calculate actual fuel consumption
Note: Driving with different driving styles can influence the adjustment accuracy!
Adjustment with ISTA
Go to Vehicle Management → Service Functions → Powertrain → Engine Electronics → Adjustment functions → Consumption calculation
Below are the exact steps I did for the problematic F25 X3.
So far, so good.
But, here comes the first problem: The difference between the displayed and the actual consumption exceeds the limit of adjustment range.
I continued with what I was offered and handed the X back to the owner.
After a few weeks, the X3 owner informed me that it was much better, but it was still not as it should be – the predicted range after filling to the brim was about 50% off, on the optimistic side. Since I didn’t have a solution at the time, I did what all service consultants do: we made an appointment for the software update.
So, here’s what happened after the software update.
The fuel consumption indicator was almost 100% correct, but the range prediction was still way off.
Then it struck me.
I know that my wife’s X1 Diesel can make some 400-450 miles with a full tank, but when I drive it and take it to the gas station, after the filling the range prediction is always about 550-600 miles.
The reason lies in driving style. When I drive, it is usually on a motorway at a constant, cruise control speed. When I arrive at a gas station, the engine electronics remembers the consumption and calculates the range prediction according to the current state.
It is nothing new, and we all know this. But, then I discussed it with the X owner, and we came to the same conclusion.
As I promised, here’s the guide to adjusting the fuel consumption via the instrument cluster hidden menu:
BMW Hidden Menu Fuel Consumption Adjustment
1. Turn the ignition on by pressing the start/stop button while holding down the odometer reset button.
2. Release the odometer reset button, and a choice of four options should appear on the dashboard. Use the odometer-reset button to go to the next entry with a short press and to select with a long press from here on out.
3. Select the option that says Unlock through the above, and you’ll be sent to a passkey screen. Your passkey is the sum of your VIN’s last five digits. Increase the two-digit number until you reach it, then select it with a long push of the odometer button.
4. Scroll down to the correction factor and change the value from 1000 to whatever you need.
Make a correction over 1,000 if your trip computer reads higher than the true figures calculated. Make the adjustment number under 1,000 if your trip under reads. The adjustment will work as long as you stay in the permissible 12% up or down range. So, if your consumption indicator shows 10% better MPG than actual, you should adjust it to 1,000 minus 10% = 900.
Below is the guide on how to access the hidden menu.