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BMW i3 REx Coding

If you have looked at getting an i3 REx, you will know that the US version is extremely limited in how it uses its gas engine.  The European version has a mode to hold charge instead of using battery first.  Coding is how we acquire that feature in the US model.

To code the car you need a few things:

  1. Smartphone with BimmerCode (Paid version, was $34.99 through Google Play)
  2. Supported OBD-II Adapter (Generic won’t work, see full list at BimmerCode, I used the following):

Once you have your adapter and BimmerCode configured and connected:

  1. Within BimmerCode select the ECU labeled Headunit and select the option for: range extender menu
    1. NOTE: Save your settings first, this one will clear a lot of your head unit settings.
  2. Tell Bimmercode to Code, and the center display will reboot
  3. If you want to extend gas tank size to 2.2 Gallons
  4. Select option in ECU labeled Instrument Cluster for: increase electronically limited fuel capacity

After you code the Instrument Cluster it will throw several errors as it reboots the center display.  I powered off and on after this was done and everything was clear.  I used only basic programming options so didn’t try to enable the full 2.4 Gallon tank or anything more advanced.

In normal operation the BMW i3 REx drains the battery to 6.5% and turns the engine on.  As it drops down to 0.5% it uses the engine more and more.  Once you hit 0.5% you are running only on the engine.  This is a motorcycle, no scooter engine with about 34 hp (25 kW).  It doesn’t have a lot of go power, most modern 3000 lb cars have over 100 hp, so 34 hp might be adequate to move a motor scooter at highway speeds it isn’t suitable for a car at those speeds.

Once coded we can set the car to hold state of charge starting at 75% or less (This feature can’t be enabled until state of charge is 75% or less).  When the feature is engaged, the car tries to hold the battery state of charge, and if it is unable to it will still run the engine and use the battery for any extra power required. Warning: Must reengage this feature every time you exit vehicle.

Using the great calculator at ecomodder, you can see that speeds of 80 mph require 25 kW of power to move on flat ground with no wind given my assumptions.  Realistically, the car will do 70 mph in those situations, but any headwind or hill will dramatically reduce the speed the car is able to maintain.

MPH KM/H % Aero % Rolling Watts
50 80 59.00% 41.00% 8,002.04
55 89 63.52% 36.48% 9,892.78
60 97 67.45% 32.55% 12,095.11
65 105 70.86% 29.14% 14,637.35
70 113 73.82% 26.18% 17,547.82
75 121 76.40% 23.60% 20,854.86
80 129 78.65% 21.35% 24,586.77
85 137 80.61% 19.39% 28,771.91
90 145 82.34% 17.66% 33,438.57
95 153 83.86% 16.14% 38,615.11

If we take 70 mph as the max the car will hold on flat ground, and you want to drive 80 mph instead, that means the car is going to need another 7 kW of power.  This excess power will come from the battery and augment what the gas engine is providing, so the extra power to maintain 80 mph the battery at 75% (approx 14 kWh usable) could last about 2 hours (160 miles) until the buffer depleted from 75% to 0.5% (you will need to stop for gas of course as it will run out first).

On a 210 mile trip, I was able to drive 185 miles with most of my highway driving at 77 mph and still have about 40% buffer to finish off the last 25 miles to my house (I turned off hold mode when my remaining EV range exceeded my distance home by a few miles).  I had no slow downs and no stress worrying if I would make the next gas station like I did when I was running un-coded (as I always had the remaining buffer I could dip into if necessary).


If you buy an i3 REx in the US, I would definitely recommend “Coding” it to unlock the European tank capacity and Hold mode.  It really makes the car far more useful for trips.

6 thoughts on “BMW i3 REx Coding Leave a comment

  1. Sorry your information is incorrect. i3 DOES NOT RUN on engine. The motor bike engine is used as a generator. This programming does a lot of harm to the vehicle on the mid to long run. Even though engine is a motor bike the rest of the system is not designed that way. Don’t you think that having systems that Europe use will not work effectively in a heavily control emission system like US has? Also what kind of damage it can cause, Iv seen this a lot (system logs most modifications) and people rather believe the internet than the people actually deals with the product. If you are unlucky 2-5 years down the line be ready for a HV battery overhaul. Email is bs, Just wanted to spark some thought from you. You spread half-truth information that can put individuals in a bad situation. All the information you put out is correct but there is no reflection of negative effects.

  2. Both comments are partially correct. 1. Rex is a generator, output is 34 hps and it generates 24 Kw electricity to drive the I3. At 24 KW , Top speed for i3 is around 115-120 km/h, or 70-75 mph, while batter power is good for ~150 km/h, or 92 mph. 2. Rex fuel tank is the same between European version and American version at 9 liters. To qualify for California EV incentives that gas powered vehicle distance cannot be greater than battery powered range. So BMW use software to control how much gas can be consumed. Therefore there is harm in removing the fuel tank restriction. In fact since 2017, with the larger battery capacity, BMW removed tank size restriction code. 3. North American Rex generator engine is tuned exactly like European counter part, no better and no worse.
    My comment: Rex is a backup system so one doesn’t get stranded, why burn gas in a car that is not designed for for ICE (internal combustion engine)? I3 Rex fuel economy is rated at 6 l/100 km, not very good when comparing to most Hybrid cars out there.

  3. Thanks California for wrecking a good little car with stupid modifications.
    Why on earth can’t the rest of the nation get the program that basically the rest of the world uses? I hate running out of power on cold days and slowing to 15MPH on that last long hill. A hold charge would let me run heater and get me over that hill safely.

  4. I am likely going to be picking up an i3 on the west coast and drive to Illinois; Thanks for your adventure series which has motivated me to consider doing the long trip. I would like to code before I begin the drive from CA. The Vgate adapter is not listed at Did you find the Vgate listed at when you bought yours? Also, when I click on the adapter link you provided, I see several other options as well. Did you buy the exact one that shows up when I click the link ($21.99)?

    • They might have changed supported devices since then, I should probably update that page. I bought the one linked to on recommendation from someone else, and it worked fine when I coded the car last year.

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