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Battery goes flat

Tiny
KYLEBMW
  • MEMBER
  • 2004 BMW 745
  • 6.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 255,000 MILES
I just bought this car 745i. I am told this was a dumb idea but I love the car. Unfortunately there are numerous issues with the car all kinds of warning messages including but not limited too; engine malfunction, transmission fault, right driving light failure, seat belt and airbag failure, transmission fault and dynamic drive control failure. Can anyone tell me why it might do this? I saw on YouTube that it could be because the battery wasn't reprogrammed when replaced. Also the indicator light for the seat adjust stays on. Or does it come on when you approach the car with the key fob?
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Friday, March 15th, 2019 AT 10:46 AM

9 Replies

Tiny
BMDOUBLE
  • MECHANIC
  • 1,139 POSTS
The battery will need to be registered but will not necessarily cause all of these issues. Only if it is low in voltage. You will need to retrieve the codes in all of the modules to get a direction for diagnostics.
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Saturday, March 16th, 2019 AT 11:15 PM
Tiny
KYLEBMW
  • MEMBER
  • 5 POSTS
Comes to be that it was low on voltage and battery died.
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Monday, March 18th, 2019 AT 5:41 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Nice work, we are here to help, please use 2CarPros anytime.
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Thursday, March 21st, 2019 AT 12:10 PM
Tiny
KYLEBMW
  • MEMBER
  • 5 POSTS
Coming to conclusion the computer or power module may be bad. Scanner gets cut off and cannot read.
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Thursday, March 21st, 2019 AT 6:36 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Yep, that can cause the problem here are instructions and diagrams on how to change the ECM out. Check out the diagrams (below). Please let us know what you find. We are interested to see what it is.
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Saturday, March 23rd, 2019 AT 2:03 PM
Tiny
KYLEBMW
  • MEMBER
  • 5 POSTS
Thank you for your advice. Hmm, I will have to try that. A video on YouTube advised doing that too. I tried yesterday but the screw in the far upper left of the cover was impossible to get to so I gave up until later, We just bought a replacement for the power module in the trunk area too. And a new ECM this morning. Hoping it solves the problem. It is sad seeing the car sitting there.
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Sunday, March 24th, 2019 AT 8:57 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Yeps cars are no good when they sit, not what they were made for. Please let us know what you find. We are interested to see what it is.
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Monday, March 25th, 2019 AT 10:31 AM
Tiny
KYLEBMW
  • MEMBER
  • 5 POSTS
So no luck yet. Changed the ECU, the PCM and nothing fixed. And the battery is dead dead dead in the morning. So we put a load tester on it and it said it was bad. Its a 1000 amp battery. So we took it into AdvancedAuto for them to test. They said it had a charge of 110 volts so they kept it over night to charge it, said it was still good but just needed charging. We picked it up this morning, reinstalled it in the car and crossed our fingers and. Nothing. Everything the same, no change.
So its going to the shop Monday morning. Its a place that does the best priced BMW work in our area and they say they do lots of BMWs. So hoping and praying. I am not ready to give up on the car.
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Friday, March 29th, 2019 AT 4:26 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Good work. it sounds like you have a draw taking the charge out of the battery. Can you please shoot a quick video with your phone so we can see what's going on? that would be great. You can upload it here with your response. This guide may help as well:

https://www.2carpros.com/articles/car-battery-dead-overnight

Please let us know what you find. We are interested to see what it is.
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Saturday, March 30th, 2019 AT 11:03 AM

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