Posts: 53
Joined: Mon Nov 11, 2019 9:37 am

Ran the REX for the first time....

Fri Apr 10, 2020 1:12 pm

Hey I coded the i3 so I could run the REX at 70%. While driving in city traffic I couldn't hear it running. But from what I have read, it is quite audible but not the case with my 2020 i3S REX.

Once I reached my destination, I left the i3 on and walked to the back and I still could barely hear it. I had to place my head underneath and place my hand at the exhaust port. This confirmed it is working away. It then ran for a short period and then shut down. So I don't know what BMW did but maybe they muffled it more.

The only clue I had when it started was a pungent smell. I have experience this smell of a brand new motorcycle engine so other than that, this works wonderfully!

Posts: 5037
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Ran the REX for the first time....

Fri Apr 10, 2020 1:31 pm

Running around, stop and go in a city, the maximum load normally wouldn't be all that high. The REx engine will adjust the RPM to help match the load. It's quite possible that it would run fairly slowly under those circumstances. Take it out on the highway, blast up a long grade, and your results will likely differ. But, there'd be more wind and tire noise, so you still may not hear it.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV
Soon (hopefully!) A 2021 X5 45e will replace the above

Posts: 64
Joined: Sat Mar 07, 2020 6:15 pm

Re: Ran the REX for the first time....

Sat Apr 11, 2020 9:59 am

The REx normally turns off when your speed is below 10 kph (unless your battery charge is below 3.5%).

One way to listen to the REx when the car is parked is to put it in the emissions test mode. The SOC has to be below 75%.

Get into the car and close the door.
Press the trunk release button
Press the Start/Stop button (BRAKE NOT PRESSED)
Press and hold the accelerator pedal.
Press and release the brake pedal.
Press and release the brake pedal again.
Press and hold the brake pedal.
Release the accelerator pedal.
Press the Start/Stop button.

The REx should start up and run at low idle.
If you press the accelerator pedal the REx switches to high idle.

The REx will stop in 20 minutes or when you press the Start/Stop button.

Be sure to get out of the car and re-close the trunk when you are done.

Posts: 53
Joined: Mon Nov 11, 2019 9:37 am

Re: Ran the REX for the first time....

Sat Apr 11, 2020 12:08 pm

OK thanks for the routine...I will save this for future reference.


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Contact: Website

Re: Ran the REX for the first time....

Wed Apr 15, 2020 5:44 am

There seems to be a lot of variation between i3s with regard to the noise made by the REX. Mine is barely perceptible, but I've seen others complaining about the droning noise.

If the little white triangle in the charge indicator jumps from 8% to 70% (or whatever your state of charge was when you switched the REX on) then the REX is running, whether you can hear it or not.


Posts: 24
Joined: Thu Jul 30, 2020 11:49 am

Re: Ran the REX for the first time....

Fri Aug 21, 2020 10:50 am

I ran the range extender for the first time after buying the 2018 a month ago. I coded the car yesterday to allow it. I did not want to depend on it with 6% remaining without trying it first. Texas is a big place!

For the first 30 seconds, there was some small vibration that caused metal items in the driver's door pocket to jingle. After that, there was no vibration and I could not hear it over the radio. I ran it for the 5 miles to my take-out breakfast stop.

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