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Discussion Starter · #1 ·
Hey all,

Left my lights on overnight and didn't realize it馃槗, battery died out and wouldn't start. Got the car jumped and finally turned it on and had a service engine soon light on, let it run for 10 minutes before driving so the alternator could charge it back up. Turned car off, got back in it later the same day, drove and the light was still on. Next day the same thing- drove, SES light on, turned car off. Today, drove to the gym (SES light on) turned car off, finished a workout, came back out, turned the car on but the SES light was now off. I was going to take it into the dealer to get it scanned but remembered I had a scanner in the car, scanned the car and got engine code: U0100-Lost Communication With ECM/PCM. This is no problem right? Considering the battery died, it's obvious that there was lost communication with the ECM? Just wanna make sure. Another note: did have an inspection done in April 2020, all they said was they recommend a battery change because the battery has been in since 2012. Car is a stock 2008 335i. Thank you for any help.
 

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Resident Curmudgeon
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I agree with your assessment. HOWEVER, once the battery is on its downhill slide, just running the car for 30 minutes, or even a longer drive, may not be enough to recover it. Id get a new batter- easy to do. Then register it, clear codes and carry on!
 

Happily Driving
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I agree with your assessment. HOWEVER, once the battery is on its downhill slide, just running the car for 30 minutes, or even a longer drive, may not be enough to recover it. Id get a new batter- easy to do. Then register it, clear codes and carry on!
Do the 2008 models require registration?
 

Registered
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Discussion Starter · #5 ·
I agree with your assessment. HOWEVER, once the battery is on its downhill slide, just running the car for 30 minutes, or even a longer drive, may not be enough to recover it. Id get a new batter- easy to do. Then register it, clear codes and carry on!
Sounds good, batteries are just so expensive though 馃槄
 

Resident Curmudgeon
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Nuclear engineer
02/2012 X5 35d M57Y CPO 105K miles NOKIAN WR G3 20K miles
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Hey all,

Left my lights on overnight and didn't realize it馃槗, battery died out and wouldn't start. Got the car jumped and finally turned it on and had a service engine soon light on, let it run for 10 minutes before driving so the alternator could charge it back up. Turned car off, got back in it later the same day, drove and the light was still on. Next day the same thing- drove, SES light on, turned car off. Today, drove to the gym (SES light on) turned car off, finished a workout, came back out, turned the car on but the SES light was now off. I was going to take it into the dealer to get it scanned but remembered I had a scanner in the car, scanned the car and got engine code: U0100-Lost Communication With ECM/PCM. This is no problem right? Considering the battery died, it's obvious that there was lost communication with the ECM? Just wanna make sure. Another note: did have an inspection done in April 2020, all they said was they recommend a battery change because the battery has been in since 2012. Car is a stock 2008 335i. Thank you for any help.
If you ran your car, driving it or not, 24/7, it would not charge the battery significantly. The battery is charged ONLY on overrun, trailing throttle or spin-down of the alternator. Otherwise, usually, normally, FOREVER, the alternator is ONLY maintaining the accessory loads, keeping battery current ZERO.
 
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