i3 rex runs for 10-15 mins then shuts down

[AJDavies21]

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!

Regards

Andrew

 

[Anonymous]

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??.

 

[AJDavies21]

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]

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.

 

[AJDavies21]

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

 

[Dvoid]

I am now having this problem with my 2015. What was your end result?

 

[Dvoid]

Turned out to be a bad spark plug, setting off a sensor. Easy fix.

 

[helpmycar]

Hey, glad you got it sorted. I'm having a similar issue with my 2013 i3 rex and was wondering if you could elaborate any more on the faulty spark plug causing a sensor error - namely was there any fault codes prior to replacing the spark plugs and also do you know what sensor was causing the error, just because I'm getting a fuel tank pressure and crankshaft sensor error codes.

 

[alohart]

also do you know what sensor was causing the error, just because I'm getting a fuel tank pressure and crankshaft sensor error codes.

The fuel tank pressure sensor is prone to failure. Apparently, BMW USA has extended the warranty for this pressure sensor and has been replacing it at no cost.

 

[spartacus68]

If REx not engaging I would renew spark plugs and fuel pump relay as a matter of course.