View Single Post
Old 10-04-2012, 06:53 PM
Yorgi's Avatar
Yorgi Yorgi is offline
Officially Welcomed to the 'Fest
Location: Toronto
Join Date: Mar 2005
Posts: 3,650
Mein Auto: '04 M3 / '06 650i Cab
Originally Posted by avoiceoreason View Post
...1) I know the alternator doesn't engage (and therefore charge the battery) under a certain speed. What is that speed?
Not sure where you heard that but I am almost 100% certain this is not true. It would mean the car does not charge when at idle and I know it does charge at standstill.

Originally Posted by avoiceoreason View Post
I have a short commute and touch maybe 45 for a few minutes at best. Of course I wasn't commuting at all prior to the last month and the car would go days at a time without being driven (which you would think would be the problem) - no problems - then when I start driving more regularly I get the error.
The short trips are your big issue. The car stays awake for 30-45 minutes at the end of the trip and drains the battery. If you don't take 30 min trips on a regular basis the battery will eventually go flat. BMW calls it an "unfavorable driving profile" if you take short tips daily and try to blame it on you instead of admitting the majorly screwed up on the design of the electrical system on these cars.

If you battery is going flat in a few days after a charge you have an issue. Either:
1) you are not fully charging it (it will take at least overnight to charge with a trickle charger)
2) the battery is not holding a charge (battery is sulfated and needs replacing)
3) there is an issue with the cars charging system - alternator is on the way out/bad connection to alternator or battery/serpentine belt is slipping.
4) there is some system not shutting off and draining the battery

A good mechanic will be able to determine what is going on. You need someone to hook up the alternator to a oscilloscope to test it. Battery is easy to load test. Most mechanics are too lazy to test that connections are good.

No idea about the fob, I don't have comfort access.
Straight lines are for fast cars...turns are for fast drivers
'04 M3 - track
'06 650i Cab - daily driver
'02 Highlander - kid hauler
'01 330Ci - winter beater

Reply With Quote