REX little mistery

[brubix]

I drive my i3 REX since August 2014.
In more than 70.000 km I tested the car (and the REX) in all kind of situations, and I think I know pretty well what I can expect. Honestly, I truly believe this is an amazing car, practically with no limits (if only the REX could offer a little more power and the tank a little more capacity, but this is another matter).

Not a single a problem so far, except the following, which appeared for the first time a few months ago (about at 60.000 km).

Highway on the plain, speed around 120 kmh, battery goes under 5% (approx.) and the REX turns on.
For 15-20 minutes the car slows down to a speed as low as 35 kmh up to 70 kmh maximum.
Then it can accelerate again even to the top speed, if the battery still has some juice.
Never had this problem before: the car always could (and still can) run at least at 120 kmh even when the battery goes to zero (except during those 15-20 minutes).

I would think to the ageing of the battery but what makes me really puzzled is that this happens only if the gasoline tank is full !
Same pattern, but with the tank at 3/4 and the problem doesn't occur.
In fact, the only thing that changes in those 15-20 minutes, is the fact the tank progessively empties from full to 3/4 (approx.)
Moreover, if I stop to refuel and resume the trip with the battery still very low (obviously) the problem doesn't occur a second time.

Here a you can see a few pictures of what the display shows when the condition is "active":
https://drive.google.com/drive/folders/17nxe5zPMQm4wsXsz4RErHjNNq0b3Pwb5

Local service has already checked the car and got in touch with the country headquarter's engineers but all they could offer are a few silly explanations that do not explain the observed behavior.

Any thought?

 

[tjburbach]

This sounds a lot like the state of charge issue that some others have run into where the i3 is not correctly measuring the condition of the battery. Here is an article about it with the related service bulletin numbers. However it does seem odd that the service technicians would not already know about this.

http://bmwi3.blogspot.com/2017/03/incorrect-state-of-charge-readings.html
-Tim

 

[tjburbach]

I rushed to reply after looking at your photos but reading the post again in more detail the failure you describe is different than the state of charge. I wonder if your failure is related to the fuel tank pressure sensor causing the Rex to not run at the rpm required for the speed you are driving. Then after the tank gets to 3/4 full and you depressurize it to fill the tank up the sensor works correctly, for some amount of time. One experiment I can think of would be to get into the failing condition with a full fuel tank, then stop and use the pull handle to manually depressurize the tank and open the tank fill cap. Close everything up and try running again to see if the behavior changed.
-Tim

 

[tjburbach]

I was looking over the Rex document thinking about this some more. The technical documents mention that the Rex goes through a warm up cycle that can last up to 360 seconds at up to 2400rpm (the speed it would normally run to maintain a vehicle speed of 50km/h).

In order to bring the combustion engine and the catalytic converter to operating temperature, the
combustion engine is operated at a speed of 2,200 rpm - 2,400 rpm during the warm-up phase
(5). This is dependent on the speed driven and, at the same time, represents the idle speed of the
combustion engine. The period for this warm-up phase is roughly 360 seconds depending on the
ambient temperature

The graphs imply that as the state of charge falls the Rex rpm should increase in order to make power to charge the battery. One possibility then would be that the Rex is staying in the warm up cycle (the system believes that the SoC is high enough to spend time warming up the emissions system). Another possibility is that the Rex thinks the ambient temperature is too high and is reducing rpm in order to attempt thermal management control. What is the current weather conditions where you are driving?
-Tim

https://attachments.priuschat.com/attachment-files/2016/07/108943_12_W20-Engine.pdf

 

[brubix]

Thank you for your interesting remarks.
I forgot to mention that BMW already replaced the tank sensor.
It always happened in mild (or not-so-cold) weather. Last time must have been around 5-6° Celsius, but before it certainly happened in warmer days.
What I find really puzzling is the "full tank" factor. I definitely try your suggestion to manually depressurize the tank and I'll report back (although it will take a few days since I'll be traveling [by train !] in the next days).

 

[brorob]

I wonder if something is malfunctioning with the thermal cooling system for the batteries. The batteries could be getting too hot then cooling down to a normal operating temperature during the reduced speed duration which would give you full power again. The reason I suspect this is when it was really cold out and I just started driving, without any departure time or preconditioning, my power band would only show a few bars until the batteries warmed up from driving. Could be just the opposite happening to you.

Would be interesting to see the battery packs temperature when this happens.

 

[brubix]

Is it possible to see the temperature of the batteries ?

 

[alohart]

Is it possible to see the temperature of the batteries ?

"batterietemp" is item 14.05 in the Service Menu. Search for "service menu" to learn how to access it.

 

[brubix]

First report. Upon my insistence they checked again and this time they "calibrated a sensor" and "re-programmed the car", whatever this means. I downloaded my profile to a usb key and now I see <i-step>I001-17-11-543</i-step>, if this is the current version. Unfortunately I cannot tell which version I had before.
I've just made a short test in the same conditions (tank full, exhausted battery, speed > 100 kmh) and the problem did NOT appear.
Next week I'll make a second, more demanding, test on a longer trip, when I'll be able to drive the battery down to zero.
However in the past, the problem manifested right after the REX turned on, and the battery still had some charge (4-5%).
Thanks to everybody !

 

[tjburbach]

Hope the "calibration" fixes the problem so that you don't have to worry about it any longer.
-Tim

 

[brubix]

Second test yesterday, with the same itinerary and under the same conditions that induced the problem in the past.
This time everything went fine: at 6% SOC the REX turned on and it was able to keep me driving at 118-122 kmh till I reached my destination (about 60km), and, at the same keeping SOC over 2%.
Excactly what I was used to until a few months ago.
https://drive.google.com/open?id=1szU8EVI3U_7fC2n7U24OrB_NW2Hxdz42

External temperature was 3.5°C, battery temp. 20°C. Must have been more or less the same last time I had the problem.

And now I'm sure that they updated the software because a new, funny bug appeared: as you can see in the photo, the white dot showing the charge/discharge intensity is ALWAYS at 100% charge (all to the left) ! Even accelerating or driving at 3 kmh ...
It just go back in the middle only when the car is completely stopped.

Side note: the ePower blue bar shrinks dramatically as when I had problem. I cannot say how it behaved under the same conditions when the car was new.

Thanks to everybody !

 

[brubix]

For those who are interested, the saga continues ...
After two successful tests in the past days, this morning, in the same conditions already described, the "problem" happened again.
But with a "nice" addition.
So ... the car slowed down as "usual". I stopped to check if removing the fuel tank's lid would help (as suggested by tjburbach). It didn't.
I also checked the battery's temperature: 20° C (outside was 2.5°).
I drove a couple of km more at 40 kmh, then I stopped again.
Bang ... the REX turned off automatically signaling "Engine group. Slow down and stop".
I still had 5% SOC but the car was unable to move and the REX never turned on again.
I waited for the tow truck and had the car brought to the local dealer. There the car was almost completely dead and we had to connect a supplemental 12V battery just to put it in Neutral mode and push it back.
It's unlikely that the 12V battery completely drained during the wait, also because I still had some charge in the high voltage battery: I guess that 1% is enough to run the blinkers for years.
Most probably it was already near to die and I suspect it was the real problem since the beginning.

 

[spinball]

Are you saying the current problem is a dead 12V battery?

 

[brubix]

No, I just tried to explain that:
a) today the REX shutted down suddenly and later I've found that the 12V battery was dead (I cannot tell if this has been the cause or what was the state of the battery when the problem occured)
b) the 12V battery was probably not in a good shape (3.5 y/o) and this MIGHT have been the cause of the problem I've described in my first post (which only happens since a few months)

 

[tjburbach]

It will be interesting if a new 12V battery corrects the issue. If so it may be one more reason to change the i3 battery out on a schedule rather than waiting for it to die like you would in a normal car. It is interesting to think about how the starter motor in an ICE car can quickly give feedback about the health of a 12V battery and all the new hybrids miss this. I wonder if in the future automobile manufacturers will need to add a 12V battery test load and a routine to check the battery condition and report back to the user/service depot... Then again that is one more system to fail.

 

[spinball]

OK. A dead/dying 12V battery causes all sorts of weird issues in this car and unfortunately some of them are severe.

 

[brubix]

OK. A dead/dying 12V battery causes all sorts of weird issues in this car and unfortunately some of them are severe.

Was this a well known problem ?

 

[spinball]

I don't think the 12V battery goes dead more frequently than in any other car, but the way the symptoms appear in the i3 can be very different. If it's dead you may not even be able to get the car out of park. I guess that's no different than a gas car not being able to start the engine if the 12V battery is flat dead but like tjburbach said, you'd usually notice that the starter is sluggish before it's too late.

I think the car should do a better job of recognizing when the battery isn't charging properly or is dying and inform you before you get stranded.

 

[brubix]

Very different , indeed. At least in my recent experience.
With an ICE car you might not be able to turn the engine on but until the engine is running you should be ok.
In my case the REX was running and when I stopped the car it was turned off automatically and ... puf ... I got stuck, although most probably it was not the state of the 12V battery that caused the shut down, in fact the REX is often turned off when the car stops.
Ironically enough I still had 5% in the high voltage battery, enough even to drive the car for a few km but apparently it cannot recharge the 12V battery.
In any case the car refused to move even for a few meters.
I got a new battery and will try test again "my problem" next week and will report back.
Thanks !

 

[brubix]

Updates.
I've made a couple of tests in the last days, including one with the same itinerary and the same conditions of the last "problem".
Everything worked as expected: at 7% SOC the REX started and I was able to drive at 140 kmh until SOC reached 2%.
Then the car gradually slowed down to 121 kmh and the REX seemed to be able to keep SOC at 2%.
At 115 kmh the REX was able to recharge till 4% (when it seems to me that it has reduced the RPM instead of keep charging).
This is completely consistent to what I was used to.
It remains a mystery to me how the problem can have been caused by the 12V battery, especially the fact that it happened only if the fuel tank was full.
The only thing that I can say is that as soon as you notice problems with the REX, check the 12V battery.