Rex 2014 not working when battery is about 6% low

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Maria P

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Feb 8, 2024
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So I was driving the other day and I had pretty low battery about 10% and suddenly I had to accelerate more than I expected, and I think the battery went too low because the vehicle started to move at the lower speed no matter how much I push the accelerator. I tried to use the range extender, but it will just not kick in. I ended up stopped in the middle of the road and I had to take the car to the garage with a truck.

BMW dealer said it was the 12v battery which was never changed in 10 years so I was thrilled 🤩 … like wow this is great for a 170.000 km / 105.000 miles car

I went to pick up my car and drove with the rain extender to many places combining obviously with the battery but never going that low again until one day a week after I got the car back that I decided I was gonna wait until the range extender kicked in automatically when it reached 6% battery low and to my surprise, I had the exact same issue and I had to get the truck to take the car to the dealer again .

They had it for a week and they were unable to tell me what was going on. I have been using the range extender with about two or 3% battery and never had any issues although I didn’t drive too fast for obvious reasons. it kind of feels to me that after so many kilometres when it says 6% battery, it might be less than that cause when I’m using it with more battery than that it works absolutely perfect. I just wanted to know if anybody had any issue like this before and if you have any clue of what could it be since my dealer had no idea and now I need to look for other options. Thank you
 
Your issue has been experienced by quite a few early i3 owners. The problem is that the battery management system (BMS) has computed an incorrect charge level at low charge levels so that the BMS will reduce the battery pack's maximum power output to protect its battery cells from being discharged too much.

When this happens, you should be able to see propulsive power bars on upper right section of the power gauge disappearing one by one until there are no power bars remaining. At this point, an i3 will not propel itself. It's better to stop in a safe location while some power bars remain. I always pay attention to the power gauge at low charge levels for a warning when our i3 is about out of power.

The BMW Blog describes this problem. BMW's Service Information Bulletin SI B61 20 16 POWER LOSS AT VERY LOW SOC OF HV BATTERY and SI B61 21 16 SERVICE ACTION: PROGRAMMING CONTROL UNITS (RANGE) describe the problem and the fix. However, these SIB's seem to limit this fix to i3's manufactured only in 2014. Maybe there are later updates to these SIB's that would cover later i3's, or maybe this problem is limited to system software versions (a.k.a., integration levels) earlier than I001-16-03-50x (March, 2016). I suggest asking your dealer whether the fix described in these SIB's, a system software or integration level update, would apply to your i3. Unfortunately, a dealer would probably charge a few hundred dollars for a system software update.
 
So I was driving the other day and I had pretty low battery about 10% and suddenly I had to accelerate more than I expected, and I think the battery went too low because the vehicle started to move at the lower speed no matter how much I push the accelerator. I tried to use the range extender, but it will just not kick in. I ended up stopped in the middle of the road and I had to take the car to the garage with a truck.

BMW dealer said it was the 12v battery which was never changed in 10 years so I was thrilled 🤩 … like wow this is great for a 170.000 km / 105.000 miles car

I went to pick up my car and drove with the rain extender to many places combining obviously with the battery but never going that low again until one day a week after I got the car back that I decided I was gonna wait until the range extender kicked in automatically when it reached 6% battery low and to my surprise, I had the exact same issue and I had to get the truck to take the car to the dealer again .

They had it for a week and they were unable to tell me what was going on. I have been using the range extender with about two or 3% battery and never had any issues although I didn’t drive too fast for obvious reasons. it kind of feels to me that after so many kilometres when it says 6% battery, it might be less than that cause when I’m using it with more battery than that it works absolutely perfect. I just wanted to know if anybody had any issue like this before and if you have any clue of what could it be since my dealer had no idea and now I need to look for other options. Thank you
A related story. I was driving merrily down the freeway this week and saw an i3 on the side of the road with flashers on. So I pulled over and asked the driver if I could help. Well, the 2015 was low on power and REX wouldn't turn on. She had already called for a tow truck. I realized I did not know what to do to help the situation. My i3S is REX-less (my 2014 i3 had a REX that worked fine when i traded it in). I don't have any i3 jumper cables :) so I wished the frustrated driver good luck. Is there anything I could have done?
 
I suppose you could have tried to start the REx engine in emissions test mode. If it started, you could have pressed the power pedal to increase the REx engine speed enough to charge the battery pack a bit. Maybe that would have been sufficient for her to drive home.

However, if the REx engine wouldn't start, it would need to be repaired, so there wouldn't have been anything that you could have done.
 
Your issue has been experienced by quite a few early i3 owners. The problem is that the battery management system (BMS) has computed an incorrect charge level at low charge levels so that the BMS will reduce the battery pack's maximum power output to protect its battery cells from being discharged too much.

When this happens, you should be able to see propulsive power bars on upper right section of the power gauge disappearing one by one until there are no power bars remaining. At this point, an i3 will not propel itself. It's better to stop in a safe location while some power bars remain. I always pay attention to the power gauge at low charge levels for a warning when our i3 is about out of power.

The BMW Blog describes this problem. BMW's Service Information Bulletin SI B61 20 16 POWER LOSS AT VERY LOW SOC OF HV BATTERY and SI B61 21 16 SERVICE ACTION: PROGRAMMING CONTROL UNITS (RANGE) describe the problem and the fix. However, these SIB's seem to limit this fix to i3's manufactured only in 2014. Maybe there are later updates to these SIB's that would cover later i3's, or maybe this problem is limited to system software versions (a.k.a., integration levels) earlier than I001-16-03-50x (March, 2016). I suggest asking your dealer whether the fix described in these SIB's, a system software or integration level update, would apply to your i3. Unfortunately, a dealer would probably charge a few hundred dollars for a system software update.
@alohart This is great information. I’ve never paid attention to the power bars. I most definitely will now. I try my best to learn as much as possible about Bailey I3. This is super helpful.
 

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