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SHRNTA

BMW e39 525i Trans fail safe

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Hi everyone,

Couple days ago the red battery light came on the dash and now I have potential battery drain issues. As I remember the following happened in order:

  • radio flickered
  • battery light came on
  • instrument cluster warning lights (ABS, DSC etc) came on
  • *Trans fail safe mode activated
  • radio switches off

I managed to coast home, pulled out my multi-meter and the battery voltage was 8v. I don't use the car much so the battery was was on charge overnight before driving on the day. I was driving for a good couple hours on the day before the issues started.

I'm thinking I maybe I have a voltage regulator issue. I checked the alternator and it was putting out 14.v when the car was running. I also checked the battery charge when the car was running and it was around 18v, hence thinking its a bad voltage regulator.

I recharged the battery now at 12.7v, started the car (battery light still on), but everything else was working (radio, no other warning lights on the dash). However when I put my foot on the accelerator again *trans fail safe mode kicked in, radio switched off dash lights came on. Now I'm 80% sure it's the regulator based on this however, this morning when I went to start up the car it wouldn't start and the multimeter read 0.1v so battery drain as well.

Just wanted to know that my thinking is right about the voltage regulator and it needing to be changed, hopefully sorting out the *trans fail safe mode and battery light issue, but will this also be the reason behind the potential battery drain issue (as in a faulty voltage regulator can cause battery drain)?

 Thanks

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yes a faulty regulator could possibly cause a battery drain, depending on how it has failed, you also need to consider whether the faulty regulator killed the battery, or did a knackered battery kill the regulator?

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