AJDavies21
Posts: 3
Joined: Sun Apr 25, 2021 12:10 am

i3 rex runs for 10-15 mins then shuts down

Sun Apr 25, 2021 12:39 am

Hi - I have a 2015 i3 with a REX, I've had it for 2 years with no major issues, until a few weeks ago where I got an amber warning saying the rex had stopped working - continue on electrical charge only. Normally this wouldn't be a problem, but on the occasional days I now commute to the office (88 miles round trip) I need the Rex for the last 8 -10 miles of my journey. Interestingly the REX is kicking in when it should but after 10-15 mins of driving turns off. The first time this happened I restarted the car which seem to clear it, but eventually it refused to restart. The car had to be towed to our local BMW service place where supposedly they diagnosed it as a mixture of the auxiliary battery (in the frunk) needing changing - which they did, and more randomly they said there was a known fault with a part of the REX circuitry which they replaced under a recall - I'd never been informed of this, but wasn't complaining.

Hoping all was fixed, I headed off on my once a week commute, all was well, the REX kicked in on my homeward journey and I was literarily thinking all was good when the dreaded message reappeared...luckily I had 5 miles of stated electrical range left and made it back home where I recharged the car on the drive. The car goes back into BMW on 10th May.....they've asked me for suggestions as to what might be wrong....

I may go through the (somewhat odd) procedure of getting the REX maintenance cycle to kick in and see it it lasts the full 20 mins...

So to recap - REX kicks in as it should but after 10-15 mins shuts down - maybe some sort of thermal protection issue? If anyone has had any similar issues, or suggestions I can pass on to BMW it may result in my bank account being emptied more slowly! :D

Regards

Andrew

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MKH
Gold Member
Posts: 843
Joined: Fri Nov 02, 2018 5:48 am
Location: Dallas

Re: i3 rex runs for 10-15 mins then shuts down

Sun Apr 25, 2021 4:18 am

REx oil and coolant levels checked?

Oil of course checked through port in the cargo floor/engine cover. To check coolant, you need to remove the cargo floor/engine cover. You will see a domed cap with a triangle and thermometer printed on it for the coolant (don't put just any antifreeze in - requires a specific BMW coolant). Also check the electric machine coolant level in the frunk.

When you did the test run of the REx, does the electric cooling fan come on, then stay on for a bit after the REx stops?

When the engine gets to 85/95 degrees C, the thermostat should also open the valve that routes coolant from the REx through the electric machine cooling channels through the radiator - maybe that's not working??.
Last edited by MKH on Sun Apr 25, 2021 10:20 am, edited 1 time in total.
Mark H.
2015 i3 Rex, Capparis White, Tera World, Technology & Driving Assistant, Parking Assistant, Harman Kardon Audio System, 19 inch 427 wheels, EVoInnovate EVSE

AJDavies21
Posts: 3
Joined: Sun Apr 25, 2021 12:10 am

Re: i3 rex runs for 10-15 mins then shuts down

Sun Apr 25, 2021 9:19 am

Hi MKH

All valid points - thanks. It would appear I have too much charge in the battery to initiate the REX (<75% I believe) I'll take it on a few trips around the block, try the REX and report any findings.

Regards

Andrew

alohart
Posts: 2406
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: i3 rex runs for 10-15 mins then shuts down

Sun Apr 25, 2021 11:33 am

A diagnostic trouble code (DTC) must be set when the REx engine shuts off prematurely. This would result in the warning message being displayed. Your dealer almost certainly would have read the DTC which should point to the problem. If you have an OBD reader (the BimmerLink smartphone app explains the propriety BMW DTC's), I would read the DTC's and report to this forum what you discover.

One fairly common REx problem is caused by a bad fuel pump relay. The relay is inexpensive and easy to replace. However, there's no way to know whether that's the problem without knowing the associated DTC's.
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

AJDavies21
Posts: 3
Joined: Sun Apr 25, 2021 12:10 am

Re: i3 rex runs for 10-15 mins then shuts down

Mon Apr 26, 2021 12:41 am

Thanks Alohart

In all honesty, when BMW had the car initially, I think they thought changing the auxiliary battery and updating some of REX electrics would solve the issue. I don't think they let the REX run to test it - even though I told them the problem was not so much the REX starting but continuing to operate past 10-15 mins. They seemed surprised when I said the issue had reoccured.

Hopefully they'll do a proper diagnosis as you suggest this time.

Regards

Andrew

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