The BMW i3 REx model is an unusual beast, the sole example to date of a car built specifically to comply with California regulations that define it as a zero-emission electric car even though it has a range-extending engine.

That's because its gasoline range (EPA-rated at 78 miles) is more or less equivalent to its battery range (EPA-rated at 72 miles).

How does BMW manage that? By restricting drivers' ability to fill its tiny gas tank to a minimal 1.9 gallons (7.2 liters).

DON'T MISS: BMW i3 Electric Car: Why California Set Range Requirements, Engine Limits

That restriction in turn frustrates eager i3 REx drivers who want to use their cars on trips without having to stop every hour or so to add $5 or less of gasoline on long road trips.

While some i3 REx drivers swear they can do a quick fillup in less than two minutes, meaning it has minimal impact on travel time, the European version of the i3 REx has a larger tank capacity: 9.0 liters, or 2.4 gallons--enough for about 20 extra miles.

The European i3 REx also has a mode that allows users to conserve battery energy if they know high levels of power will be required in near-term future driving: on hills, for example.

2015 BMW i3 REx - Driven, Portland OR, April 2015

2015 BMW i3 REx - Driven, Portland OR, April 2015

So what's a BMW i3 REx owner to do?

At least some are choosing to follow instructions posted online and in BMW forums to "code" their cars--which is to say, modify the car's software to provide these functions.

That, not surprisingly, is highly frowned upon by BMW, for a very rational reason. Software updates could go awry, creating safety hazards from modified electronic control systems that operate every aspect of the car.

ALSO SEE: BMW i3 REx Vs Chevy Volt: Range-Extended Electric Cars Compared

Nonetheless, at least a few intrepid i3 REx owners have enthusiastically taken to coding their cars.

A partial list of functions that can be added or modified with those updates includes:

  • Allowing fuel tank to accept full capacity of 2.4 gallons
  • Adding suppressed European "hold battery charge" function
  • Enabling suppressed AM radio
  • Suppressing U.S.-mandated seat-belt warning tone
  • Permitting video to be run from USB storage device
  • Changing startup image (one owner found "a cool Alpina" emblem hidden in the car's software)

2014 BMW i3 REx range-extended electric car owned by Tom Moloughney -

2014 BMW i3 REx range-extended electric car owned by Tom Moloughney -

As we understand it, the software that enables these functions is already present in U.S.-market BMW i3 vehicles.

But it's suppressed in many cases, due to National Highway Traffic Safety Administration (NHTSA) or California Air Resources Board (CARB) regulations--or BMW North America's perception of consumer preferences.

Green Car Reports had asked the U.S. arm of BMW why it had no AM radio--especially useful for local traffic reports and news headlines.

MORE: BMW i3 Electric Car Quirk: No AM Radio--But Why?

"AM is not offered due to negative performance influences of the electromagnetic interference of the electric drivetrain," responded BMW product and technical communications spokesperson Rebecca K. Kiehne.

"While it could be offered, BMW's performance standards are very high and we don't offer a product that meets less than those high standards."

2014 BMW i3 REx vs Chevrolet Volt comparison [photos: David Noland, Tom Moloughney]

2014 BMW i3 REx vs Chevrolet Volt comparison [photos: David Noland, Tom Moloughney]

Clearly at least a few owners aren't satisfied with that explanation. The main reason for a coding an i3 REx, though, based on numerous forum posts, is the reduced fuel capacity and the lack of a mode that lets owners conserve battery charge.

Called "Hold Mode," that capability was added to the first-generation Chevrolet Volt range-extended electric car in 2013. It remains in the second-generation 2016 Volt that will go on sale in California next month.

RELATED: 2015 BMW i3 Electric Car Price Raised $1,000 To $43,350

One caveat to i3 owners who are considering "coding" their cars: Any changes may be wiped out whenever an official software update is installed by a service technician at the BMW dealer

Whether the service techs will notice the prior updates is debatable; most owners seem to feel they don't.

But be aware that messing with a car's functional software provides a carmaker ample grounds to deny warranty coverage for any condition it deems related to those modifications.


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