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I have been experiencing an intermittent problem with my beloved 2014 smart ED. The onset of this problem surfaced while using the car MUCH less due to the pandemic coinciding with lower temperatures as the winter season moved into the southern US. The dash will show "Drive Sys Off - EV Workshop" and not proceed to "Start" mode(so not turning on the HV battery). My idea was that the 12V battery was going bad. I will also note that I felt like the miles range was also reading lower than usual during this time. So fact being, my car had been running and sitting idle with an old 12v battery (the original, 7 yrs old) for how long? The error cleared and the car started after putting a charger on the 12v battery so I therefore replaced the 12v battery. It was working fine until shortly thereafter, (and still not driving much/short trips) the temperature dipped one night again and the car would not start in the morning, but would in fact start after the temp. warmed up later that day (we have had wild temp. swings like 30 degrees or more in 24hrs or less). Days later a very unusual winter storm moved into Texas and temps reached -2F and several days of sub 32F. Throughout this entire storm my car displayed the same error and would not start or accept a charge even with the new battery AND with a charger applied for days at freezing temps. So knowing that it had previously started in warmer weather, I decided to wait out the storm and try it when temps returned to around 60 degrees. After several days and 30 degrees warmer the car started! After many occurrences of this phenomena related to outside temperature persisting even after the battery being replaced I am hypothesizing that:
-The 12v system at some point becoming insufficient or intermittent due to low voltage has somehow caused the BMS and HV battery to get out of equilibrium somehow, due to a lack of 12v battery charge, lack of driving, lack of full charge cycles, perhaps explaining the low estimated range and refusal of the drive system to start in lower temps (out of threshold?). Maybe the BMS shuts down the HV after not receiving acceptable info based on historical information? Note: I used to drive this car daily with absolutely no issue in all temps. It all started when I stopped driving it.
I see similar stories on here. My HV battery was never discharged completely that I know of and since replacing the 12V battery and driving it when it's warmed up during the day lately, the range is going much higher. Days ago it was showing 50-55 miles at full charge in mild weather (too low) and today it's showing 77 at full, which seems a bit generous. I have not seen range on my car that high in a long time, so the car seems to be going through some sort of SOC adjustments. It refused to start initially this morning after several tries, but then I turned off the headlights and then it started which may or may not be related.
I will continue to monitor the car and keep a trickle charger on it during the day when it is not in use, and allow the HV battery to go through full charge/discharge cycles to see if the mysterious behavior and error relative to temperature goes away, my hypothesis being that some "bad" SOC parameters in the BMS affected by temperature brought on by the lack of 12v battery charge will go away as 12v system continues to operate correctly and the BMS corrects itself as input data is updated. In other words "was my car charged as much as it (the BMS) THOUGHT it was?" This is all assuming that the BMS is powered through the 12v system? If so, we all know that low 12v batteries can cause strange issues and when you put a BMS in the equation... who knows. Will the error ever happen again? Will it show up again next winter? According to some info on another site, these cars have a 12V draw when off between .3 - 1 amp which is more than a typical car and the 12v battery only charges when the HV battery contacts are closed(when the car is charging), or when its on of course. So lesson be, either use and charge these cars often or keep the 12v on a trickle. In theory the 12V would probably stay charged if the car is continually connected to the EVSE as the car would continually activate the EVSE to top up the HV battery, but I would prefer the car not to remain at 100% SOC for long periods. Anyway I hope the car is able to "recover" fully as time goes on and the BMS and battery are "reacquainted"?. Some other thoughts:
1. Is there a short in wiring or ground somewhere on 12v system? (Maybe, but why is starting dependent on warm temp in my case)
2. Bad relay/switch acts up in cold temps?
3. Wire harness chaffing problem (no, checked that, and not very temp sensitive)
Update 3/24/21
55 degrees out. Attempted to start car and got the error again. I then immediately turned the ignition 7-10 times and the drive system finally came on. This doesn't seem to point to software, but a short somewhere or a problematic or sticking relay. Maybe the problem is just a coincidence to the 12V battery. Also, once I get the car started and drive to a store or something, the car ALWAYS starts. The sitting overnight in cool weather (below 60) is what triggers the condition.
-The 12v system at some point becoming insufficient or intermittent due to low voltage has somehow caused the BMS and HV battery to get out of equilibrium somehow, due to a lack of 12v battery charge, lack of driving, lack of full charge cycles, perhaps explaining the low estimated range and refusal of the drive system to start in lower temps (out of threshold?). Maybe the BMS shuts down the HV after not receiving acceptable info based on historical information? Note: I used to drive this car daily with absolutely no issue in all temps. It all started when I stopped driving it.
I see similar stories on here. My HV battery was never discharged completely that I know of and since replacing the 12V battery and driving it when it's warmed up during the day lately, the range is going much higher. Days ago it was showing 50-55 miles at full charge in mild weather (too low) and today it's showing 77 at full, which seems a bit generous. I have not seen range on my car that high in a long time, so the car seems to be going through some sort of SOC adjustments. It refused to start initially this morning after several tries, but then I turned off the headlights and then it started which may or may not be related.
I will continue to monitor the car and keep a trickle charger on it during the day when it is not in use, and allow the HV battery to go through full charge/discharge cycles to see if the mysterious behavior and error relative to temperature goes away, my hypothesis being that some "bad" SOC parameters in the BMS affected by temperature brought on by the lack of 12v battery charge will go away as 12v system continues to operate correctly and the BMS corrects itself as input data is updated. In other words "was my car charged as much as it (the BMS) THOUGHT it was?" This is all assuming that the BMS is powered through the 12v system? If so, we all know that low 12v batteries can cause strange issues and when you put a BMS in the equation... who knows. Will the error ever happen again? Will it show up again next winter? According to some info on another site, these cars have a 12V draw when off between .3 - 1 amp which is more than a typical car and the 12v battery only charges when the HV battery contacts are closed(when the car is charging), or when its on of course. So lesson be, either use and charge these cars often or keep the 12v on a trickle. In theory the 12V would probably stay charged if the car is continually connected to the EVSE as the car would continually activate the EVSE to top up the HV battery, but I would prefer the car not to remain at 100% SOC for long periods. Anyway I hope the car is able to "recover" fully as time goes on and the BMS and battery are "reacquainted"?. Some other thoughts:
1. Is there a short in wiring or ground somewhere on 12v system? (Maybe, but why is starting dependent on warm temp in my case)
2. Bad relay/switch acts up in cold temps?
3. Wire harness chaffing problem (no, checked that, and not very temp sensitive)
Update 3/24/21
55 degrees out. Attempted to start car and got the error again. I then immediately turned the ignition 7-10 times and the drive system finally came on. This doesn't seem to point to software, but a short somewhere or a problematic or sticking relay. Maybe the problem is just a coincidence to the 12V battery. Also, once I get the car started and drive to a store or something, the car ALWAYS starts. The sitting overnight in cool weather (below 60) is what triggers the condition.