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Discussion Starter · #1 ·
I've been having a rather occasional problem (only happened twice so far) with my M3. The DSC, Oil, EML, and Battery lights come on and limp mode ensues. It then starts to have trouble maintaining idle. This last time, the engine died. If I turn the car off and back on, it runs fine. I didn't find any new codes.

I've read that a dying battery or bad alternator can cause such issues. I'm hoping it's the battery. It's a BMW battery (who knows how old it might be at this point?) and it's showing black in the porthole so it doesn't have sufficient charge. I did the OBC check and the voltage was at 11.7. Turned on the car and voltage read at 14.0+-0.1 (which I believe is in the lower portion of normal range). With all accessories and the headlights on it would drop to 13.9+-0.1. When I turned it back off, the battery started to drain rather quickly (about 0.1 per 45 seconds until it hit 12.5 or so, with accessories off). So, I'm thinking I definitely need a new battery regardless.

Both times limp mode came on I was driving in cold, wet weather so I had my heater, headlights, and heated seats on plus the radio. When I hit the throttle for heavier acceleration, the limp mode occurred. Exactly the same, both times. As hard as I tried, I couldn't repeat the issue on other (warmer, brighter) days.

I'm thinking a new battery might save the day. Anyone else concur or disagree? Also, should I get a new BMW battery or will an equivalent battery from AutoZone or WalMart do the trick?

Much obliged.
 

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How old is your battery? If it's close to 5 years old, replace it, and reset. Otherwise, I would disconnect the battery and test it with a VOM. If it's actually under 12 volts, then take it to AutoZone and get it stress tested under load-- if it fails that test, it has a bad cell. After eliminating the battery as the problem, I would look at the threads discussing standby current drain.
 

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Discussion Starter · #3 ·
I've only had the car for 10 months so I checked the battery for a date. Turns out, it was installed in April of '09 if the sticker is to be trusted. If that's the case, I'm surprised it lasted this long.
 

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There I was, Sicily, 1918..
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I've only had the car for 10 months so I checked the battery for a date. Turns out, it was installed in April of '09 if the sticker is to be trusted. If that's the case, I'm surprised it lasted this long.
Don't be -- they tend to last quite a while since they're not in the engine compartment... unfortunately, they tend to last "too" long, so they fail really, really slowly, causing you to chase all kinds of crap before you realize it's only the stupid battery. :thumbup:

Mine started to give me Sensor Under-voltage errors (front and rear wheels), of all things, before I thought "Hey, I last changed my battery 7 years ago... hmmm."
 

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Discussion Starter · #10 ·
Makes sense. If the battery is in the back it doesn't have to deal with all the heat from the engine. It's really odd how many issues the dying battery can cause. I wonder if any of the newer cars have similar issues.
 
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