Strange Power Loss - No Faults

[Nanniepoo]

This past weekend, due to our other car being out of commission, we took our i3 out for a long drive to visit family, deciding to just rely on the REX. Typically we don't use the REX often, but it's put in some work over the last couple weeks extending some of our drives.

REX kicked on, on the highway, on the way out, no problems.
We charged a bit at our destination, so we headed back electric only to start.
Again on the highway, the REX kicked on. Unfortunately I can't really remember the exact situation, but a little bit after, I noticed the car (in cruise control) had slowed down into the upper 50s as someone went whipping past us. I took over control, however then I noticed the "available power bars" had diminished, and we were up against it. We kept losing speed until I pulled over into the shoulder when we got into the 40s. When stopping/regenning, I noticed the bars fill back up again. Trying to accelerate, the bars dropped back down. I tried a power cycle thinking it was some weird software bug, but things did not improve. We decided safest place was not on the highway, and try to limp to the next exit. We made it on the shoulder, but basically by the time we reached the exit, it really felt like best we could do was coast. I pulled off again to allow backed up traffic to pass. Decided to push forward to at least get to a safe parking area, and we coasted in to the gas station. The best we could accelerating from a red light was 5 mph, until we hit the downhill after the intersection. A bunch of restart attempts, during which REX turned on everytime, but bars actually got worse, to where I thought we were going to be stuck as there were no bars available. Through some frantic googling, somewhere I found someone recommended starting REX in emissions test mode, which I did, and we immediately got all bars back. (of note, it sounded to me like REX started, coughed, and then started running again). Decided to use the opportunity and headed to a very close level 2 charger. Charged up for a while, but not full, and headed for home, avoiding the highway as we knew we didn't have the range. REX did kick on and everything was normal for the rest of the drive. We had our 1 and nearly 3 year old with us, so tried juggling most time efficient but safest way to get home.


Obviously a lot of things happening at once, but to me, the battery SOC looked like it was right at the REX threshold. The only reasons I could think of for power loss are:
Low SOC - I don't think this happened
Low battery temp - 77F out and had been driving a while
High battery temp - I don't think I've ever read about this happening to anyone, but did cross my mind that highway + REX charging at low SOC causing issues thermally? Still wouldn't think that would happen on a pretty mild day. And I would think that would trigger some warning? Low battery temp is pretty expected, but a high battery temperature induced derate surely should drive a warning. Also why would REX in emissions mode fix this instantly.


So my questions are:
In general, any ideas/experience with what happened?
Could my memory possibly have deceived me and REX did not start and SOC fell and that's why we lost power? Would REX not starting when it expected cause a warning or any kind?
Is it possible the REX can start but not actually charge and that's why we lost power? And would this cause or not cause a warning?


Any input is appreciated, even if it's take it to a dealer to see what they can find, because at this point I have no confidence in using the car in a situation we'd need the REX. I have ISTA for our E70, but have yet to try hooking it up to the i3. Also have a cheap, but BMW specific, scanner that I can see if there are any faults stored that wouldn't have caused any dash lights/CELs.

 

[alohart]

I'm guessing that the BMS is not calculating the charge level correctly and has overestimated the actual charge level. When your REx engine starts automatically, the charge level isn't 6-7% but is only 1-2% which is when the power bars start to disappear. The REx generator won't generate much power until the REx engine is warmed up, so during the first 360 seconds that the REx engine is running, it won't be producing much electrical power, so the charge level would not increase and might continue decreasing.

This BMS problem has happened to many i3 owners. I have read that BMW dealers had a way to recalibrate the BMS, but that doesn't seem to be something that they all do now. Some owners have tried to run the charge level down to near 0% followed by charging fully. Maybe do this a couple of cycles to try to teach the BMS what voltage corresponds to a displayed 0% and what voltage corresponds to a displayed 100%.

The best workaround would be to enable Hold State of Charge so that you could manually turn on the REx engine before the charge level drops too low, maybe at 20% or higher. The BimmerCode smartphone app communicating through an OBD to WiFi or Bluetooth adapter could do this easily.

 

[EvanstonI3]

What year is your car? What was the SOC reading when the REX kicked in?

 

[Nanniepoo]

I'm guessing that the BMS is not calculating the charge level correctly and has overestimated the actual charge level. When your REx engine starts automatically, the charge level isn't 6-7% but is only 1-2% which is when the power bars start to disappear. The REx generator won't generate much power until the REx engine is warmed up, so during the first 360 seconds that the REx engine is running, it won't be producing much electrical power, so the charge level would not increase and might continue decreasing.

This BMS problem has happened to many i3 owners. I have read that BMW dealers had a way to recalibrate the BMS, but that doesn't seem to be something that they all do now. Some owners have tried to run the charge level down to near 0% followed by charging fully. Maybe do this a couple of cycles to try to teach the BMS what voltage corresponds to a displayed 0% and what voltage corresponds to a displayed 100%.

The best workaround would be to enable Hold State of Charge so that you could manually turn on the REx engine before the charge level drops too low, maybe at 20% or higher. The BimmerCode smartphone app communicating through an OBD to WiFi or Bluetooth adapter could do this easily.

Thanks alohart! That makes a lot of sense to me.

 

[Nanniepoo]

What year is your car? What was the SOC reading when the REX kicked in?

2015
Not to sound obtuse, but REX turned on presumably at whatever SOC it's supposed to, unless the calculation was incorrect as alohart mentions. It was right at the indicator on the instrument panel.

 

[EvanstonI3]

2015
Not to sound obtuse, but REX turned on presumably at whatever SOC it's supposed to, unless the calculation was incorrect as alohart mentions. It was right at the indicator on the instrument panel.

sounds like the calculation was incorrect then. This has come up for other owners before.

 

[brubix]

Years ago I happened to repeatedly have an experience similar to yours. BMW assistance could not understand the problem. The last time this happened to me, the car refused to even start again after stopping and I couldn't even close the windows again. This way I discovered that the problem was the 12V battery (original). Once that was replaced the problem never arose again.

 

[Nanniepoo]

Years ago I happened to repeatedly have an experience similar to yours. BMW assistance could not understand the problem. The last time this happened to me, the car refused to even start again after stopping and I couldn't even close the windows again. This way I discovered that the problem was the 12V battery (original). Once that was replaced the problem never arose again.

As far as I know the battery is original (I've owned since 2018 and have not changed it). Maybe I'll do that just as preventative maintenance. Thanks!

 

[Bmwi3goandgojohn]

This past weekend, due to our other car being out of commission, we took our i3 out for a long drive to visit family, deciding to just rely on the REX. Typically we don't use the REX often, but it's put in some work over the last couple weeks extending some of our drives.

REX kicked on, on the highway, on the way out, no problems.
We charged a bit at our destination, so we headed back electric only to start.
Again on the highway, the REX kicked on. Unfortunately I can't really remember the exact situation, but a little bit after, I noticed the car (in cruise control) had slowed down into the upper 50s as someone went whipping past us. I took over control, however then I noticed the "available power bars" had diminished, and we were up against it. We kept losing speed until I pulled over into the shoulder when we got into the 40s. When stopping/regenning, I noticed the bars fill back up again. Trying to accelerate, the bars dropped back down. I tried a power cycle thinking it was some weird software bug, but things did not improve. We decided safest place was not on the highway, and try to limp to the next exit. We made it on the shoulder, but basically by the time we reached the exit, it really felt like best we could do was coast. I pulled off again to allow backed up traffic to pass. Decided to push forward to at least get to a safe parking area, and we coasted in to the gas station. The best we could accelerating from a red light was 5 mph, until we hit the downhill after the intersection. A bunch of restart attempts, during which REX turned on everytime, but bars actually got worse, to where I thought we were going to be stuck as there were no bars available. Through some frantic googling, somewhere I found someone recommended starting REX in emissions test mode, which I did, and we immediately got all bars back. (of note, it sounded to me like REX started, coughed, and then started running again). Decided to use the opportunity and headed to a very close level 2 charger. Charged up for a while, but not full, and headed for home, avoiding the highway as we knew we didn't have the range. REX did kick on and everything was normal for the rest of the drive. We had our 1 and nearly 3 year old with us, so tried juggling most time efficient but safest way to get home.


Obviously a lot of things happening at once, but to me, the battery SOC looked like it was right at the REX threshold. The only reasons I could think of for power loss are:
Low SOC - I don't think this happened
Low battery temp - 77F out and had been driving a while
High battery temp - I don't think I've ever read about this happening to anyone, but did cross my mind that highway + REX charging at low SOC causing issues thermally? Still wouldn't think that would happen on a pretty mild day. And I would think that would trigger some warning? Low battery temp is pretty expected, but a high battery temperature induced derate surely should drive a warning. Also why would REX in emissions mode fix this instantly.


So my questions are:
In general, any ideas/experience with what happened?
Could my memory possibly have deceived me and REX did not start and SOC fell and that's why we lost power? Would REX not starting when it expected cause a warning or any kind?
Is it possible the REX can start but not actually charge and that's why we lost power? And would this cause or not cause a warning?


Any input is appreciated, even if it's take it to a dealer to see what they can find, because at this point I have no confidence in using the car in a situation we'd need the REX. I have ISTA for our E70, but have yet to try hooking it up to the i3. Also have a cheap, but BMW specific, scanner that I can see if there are any faults stored that wouldn't have caused any dash lights/CELs.

Hi there ! Did you ever figure out what was going on or did you find a way to recalibrate the BMS system. Thank you

 

[Stafke]

This past weekend, due to our other car being out of commission, we took our i3 out for a long drive to visit family, deciding to just rely on the REX. Typically we don't use the REX often, but it's put in some work over the last couple weeks extending some of our drives.

REX kicked on, on the highway, on the way out, no problems.
We charged a bit at our destination, so we headed back electric only to start.
Again on the highway, the REX kicked on. Unfortunately I can't really remember the exact situation, but a little bit after, I noticed the car (in cruise control) had slowed down into the upper 50s as someone went whipping past us. I took over control, however then I noticed the "available power bars" had diminished, and we were up against it. We kept losing speed until I pulled over into the shoulder when we got into the 40s. When stopping/regenning, I noticed the bars fill back up again. Trying to accelerate, the bars dropped back down. I tried a power cycle thinking it was some weird software bug, but things did not improve. We decided safest place was not on the highway, and try to limp to the next exit. We made it on the shoulder, but basically by the time we reached the exit, it really felt like best we could do was coast. I pulled off again to allow backed up traffic to pass. Decided to push forward to at least get to a safe parking area, and we coasted in to the gas station. The best we could accelerating from a red light was 5 mph, until we hit the downhill after the intersection. A bunch of restart attempts, during which REX turned on everytime, but bars actually got worse, to where I thought we were going to be stuck as there were no bars available. Through some frantic googling, somewhere I found someone recommended starting REX in emissions test mode, which I did, and we immediately got all bars back. (of note, it sounded to me like REX started, coughed, and then started running again). Decided to use the opportunity and headed to a very close level 2 charger. Charged up for a while, but not full, and headed for home, avoiding the highway as we knew we didn't have the range. REX did kick on and everything was normal for the rest of the drive. We had our 1 and nearly 3 year old with us, so tried juggling most time efficient but safest way to get home.


Obviously a lot of things happening at once, but to me, the battery SOC looked like it was right at the REX threshold. The only reasons I could think of for power loss are:
Low SOC - I don't think this happened
Low battery temp - 77F out and had been driving a while
High battery temp - I don't think I've ever read about this happening to anyone, but did cross my mind that highway + REX charging at low SOC causing issues thermally? Still wouldn't think that would happen on a pretty mild day. And I would think that would trigger some warning? Low battery temp is pretty expected, but a high battery temperature induced derate surely should drive a warning. Also why would REX in emissions mode fix this instantly.


So my questions are:
In general, any ideas/experience with what happened?
Could my memory possibly have deceived me and REX did not start and SOC fell and that's why we lost power? Would REX not starting when it expected cause a warning or any kind?
Is it possible the REX can start but not actually charge and that's why we lost power? And would this cause or not cause a warning?


Any input is appreciated, even if it's take it to a dealer to see what they can find, because at this point I have no confidence in using the car in a situation we'd need the REX. I have ISTA for our E70, but have yet to try hooking it up to the i3. Also have a cheap, but BMW specific, scanner that I can see if there are any faults stored that wouldn't have caused any dash lights/CELs.

I've had this once with my i3-REX. The amount of charge obviously was to low, pressing gas pedal did not help, a very anxious moment. A BMW-garage was very nearby ... but they had no free time. After sitting a bit in the waiting room we decided to charge the battery. I drove to another quickcharging station in the same street but not possible to use. Because I felt the car and the REX were working I continued direction home, not on the motorway tough !!! I think an old battery at 4% can be only 2% in reality. And 3 can be 1,5 !!!

 

[alohart]

I just experienced similar but maybe more extreme behavior with a 2014 BEV that I was driving to lower its charge level to try to determine why its displayed charge level seemed so erratic (decreased or increased up to 20% overnight with no HV activity). I expected the power gauge segments to begin disappearing as the battery pack voltage decreased to near its lower limit. I was driving 55 mph at a displayed charge level of 20% with a range estimate of 12 miles when the car suddenly shut off with a drivetrain error. Fortunately, it shifted to neutral rather than park, so I was able to coast down a decline to an offramp with a red stop light at its end. When I stopped, I was able to start it again and drive normally. However, about 300 yards down the 25 mph road, the car shut off again. I was again able to restart it, but several power gauge segments were missing, so I knew that the battery pack voltage was near its lower limit. I slowly drove it toward a public charging station. Unfortunately, it shut off again before reaching the charging station. This time, when I restarted it, there were no power gauge segments and the car wouldn't move on its own. I waited at the side of the road hoping that when the battery pack cooled a bit that there might be enough power to drive slowly to the charging station. That never happened.

The eFlow app showed that the minimum cell voltage was 2.75V, way below the lower voltage limit for a cell. The average cell voltage was 3.29V which is less than the average cell voltage should be when the displayed charge level is 0%. The difference between the minimum and maximum cell voltages was 889mV which is very high. However, the BMS should not have let the cells discharge so far, so the capacity or charge level differences among these 11 year old cells having propelled this i3 for only 46k miles was obvious (76% HV battery pack state of health). At a high charge level, the minimum and maximum voltages differ by 20mV which is pretty good suggesting that the charge level balance among the cells is good.



I called a tow truck to tow this i3 to the tow truck base yard where I could plug in its occasional use cable to charge it very slowly. I couldn't think of a public charging station that I knew would be operational, available, and accessible by a large tow truck pulling an i3 that couldn't move itself. The displayed charge level had decreased to 17% by the time I started charging it at 1.44kW (12A @ 120V). After 90 minutes, the displayed charge level remained 17% which was very disappointing. However, the eFlow app showed that the difference between the minimum and maximum cell voltages had decreased to 21mV with the average voltage increasing, so charging was occurring even though the displayed charge level hadn't changed. After another 30 minutes, the displayed charge level had increased to 20%. The base yard was closing, so I needed to move this i3 or pay for overnight storage.

I slowly drove ~3 miles to 2 public AC Level 2 charging stations both of which were operational and available. I charged for 20 minutes with the displayed charge level increasing to 30%. I felt that I could safely drive another 5 miles to where this i3 was being parked while its owner was out of town. I told its caretaker to fully charge this i3 and to park it for several days so that charge level balancing could occur even though the cells seemed to be well-balanced.

I asked a certified BMW i mechanic who works at our local BMW dealer what could be done to fix this incorrect and erratic displayed charge level problem. This i3's integration level was high enough that the bug that had caused incorrect BMS calibration should have been fixed. I read that IRAP reprogramming might be necessary to fix this problem, but the mechanic told me that this was to fix a different problem and wouldn't help this i3. He told me that nothing but a battery pack replacement would fix this problem but that the cost would far exceed the car's value. Bringing it to his dealership for an ISTA diagnosis and integration level increase would be a waste of $300-$1,000, depending on how much time was spent. Unfortunately, his dealership was seeing more and more 60Ah i3's with "unstable battery cells" (whatever that means).

His recommendations were to never allow the displayed charge level to decrease below 30%, to charge whenever possible, to avoid driving up long inclines at highway speeds, and to limit driving to urban/suburban areas within Honolulu. This is not how its new owner had planned to use it, so he is very disappointed and will have to sell it at a significant loss.

 

[Chris94]

I'm guessing that the BMS is not calculating the charge level correctly and has overestimated the actual charge level. When your REx engine starts automatically, the charge level isn't 6-7% but is only 1-2% which is when the power bars start to disappear. The REx generator won't generate much power until the REx engine is warmed up, so during the first 360 seconds that the REx engine is running, it won't be producing much electrical power, so the charge level would not increase and might continue decreasing.

This BMS problem has happened to many i3 owners. I have read that BMW dealers had a way to recalibrate the BMS, but that doesn't seem to be something that they all do now. Some owners have tried to run the charge level down to near 0% followed by charging fully. Maybe do this a couple of cycles to try to teach the BMS what voltage corresponds to a displayed 0% and what voltage corresponds to a displayed 100%.

The best workaround would be to enable Hold State of Charge so that you could manually turn on the REx engine before the charge level drops too low, maybe at 20% or higher. The BimmerCode smartphone app communicating through an OBD to WiFi or Bluetooth adapter could do this easily.

Thanks, Alohart-- this info is also relevant to the thread I just posted about my Rex not kicking in when expected. "BMS not calculating the charge level correctly" sort of fits what I experienced.