Engine died while driving, bad battery or altenator?

Need some input, car keeps dying on me, throwing bunch of codes. Once it dies, it doesnt start back on. I know my battery is bad, but why is it stalling while it is idle? I hooked up a battery jumper onto my car and drove like that for 1 mile to get home safely, but once the battery jumper is disconnected, car dies.. do you guys think a bad battery would cause a car to stall at idle? or its my alternator?

Thank you!

I say alternator & possibly the battery as well. The car should be able to stay on once it's started with the charge of the alternator. The battery may also not holding a charge. I suggest getting it tested.

If you have a volt meter, put your jumper battery on and check the voltage (engine off), then check it again with the engine running. There are other ways to check voltage.. OBD tool or through the cluster.

If you see the voltage not increase, could possibly be the alternator.

thanks for the reply guys
battery voltage: 11.5
alternator voltage: 10.9 or 11 while on..
I assume its the alternator at this point.
Any idea if autozone alternator would be good compared to oem valeo?

You can save so much troubleshooting and grief if you just get a new battery.

bvrider1 wrote

You can save so much troubleshooting and grief if you just get a new battery.

Amen, try the battery first especially if it is toast

If the battery holds a charge and its running disconnect the battery while running. If it dies its the alternator.

0_to_60 wrote

thanks for the reply guys
battery voltage: 11.5
alternator voltage: 10.9 or 11 while on..
I assume its the alternator at this point.
Any idea if autozone alternator would be good compared to oem valeo?

I just replaced mine. Got Valeo for 340 online. Swap is a 10 min job super easy. Oem was $200 more. This one works great and it’s made by the same company...? No brainer

there is a battery cable service bulletin. symptoms include the car shutting off.

roastbeef wrote

there is a battery cable service bulletin. symptoms include the car shutting off.

i read it before, but i thought it didnt apply to the m3s. Any links? thanks

0_to_60 wrote

i read it before, but i thought it didnt apply to the m3s. Any links? thanks

Take a look here..
http://www.m3post.com/forums/showthread.php?t=1373697

If you want to anyway, pop in your VIN and you can see what recalls you have open on your car. HVAC blower is probably in there for you now which, I'm sure, puts a lot of load/stress on your entire electrical system
https://www.bmwusa.com/safety-recalls.html

If the car completely powers up (no other issues) with using your jumper battery, I would not suspect it being a bad cable.

I read that the alternator does not charge the battery unless the RPM's are over 3500. So when you're in idle, power is drawn off the battery, so maybe your battery is dying.

carenthuziast wrote

I read that the alternator does not charge the battery unless the RPM's are over 3500. So when you're in idle, power is drawn off the battery, so maybe your battery is dying.

Respectfully, that makes no sense to me. 90% (or more) of the time on the road, I'm under 3500 rpm.

jdamore wrote

Respectfully, that makes no sense to me. 90% (or more) of the time on the road, I'm under 3500 rpm.

I think I read somewhere on this blog where someone wrote (or referenced) that the alternator not charging the battery at low rpms allows it to be ready for when demand is required for hard accelerations/high performance demands.

Your driving situation is same as mine, which hopefully means less wear and tear on the bearings.

carenthuziast wrote

I think I read somewhere on this blog where someone wrote (or referenced) that the alternator not charging the battery at low rpms allows it to be ready for when demand is required for hard accelerations/high performance demands.

Maybe you're thinking of the AC compressor at full throttle? Anyway, that is wrong.

Keep us posted, OP.

Guys, so today turned the car on, after 15 mins of idle, i disconnected the negative battery, car died, assuming the alternator is going out. What do you guys think?

carenthuziast wrote

I read that the alternator does not charge the battery unless the RPM's are over 3500. So when you're in idle, power is drawn off the battery, so maybe your battery is dying.

i read on the forum that it was the opposite, when on full throttle, alternator disengages

that method may not be 100% good for diagnosing a problem. both the alternator and a/c can be disengaged.
and yes, the alternator and a/c disengage over a certain rpm or full throttle. i don't remember which rpm specifically.

0_to_60 wrote

i read it before, but i thought it didnt apply to the m3s. Any links? thanks

i got a letter from bmw. a google search revealed this.

https://static.nhtsa.gov/odi/rcl/2013/RCMN-13V044-3070.pdf

OP there is a bit too many variables. To help your diagnosis you want to isolate the problem. I would start with testing the battery. If you don't have one an advance Auto parts or many places will do free tests for you. Confirm the battery is good or bad and if bad replace and program it. After all that then start the car and check voltage at the battery with the car at idle. If you go from 12.6 off to 14+ running then your alternator is clearly charging. If all tests pass you may have an intermittent issue somewhere. Like others stated that battery cable recall. I remember reading another thread on here where the guy found that cable to be his issue. I will search for it.

eatsleepboost wrote

I remember reading another thread on here where the guy found that cable to be his issue. I will search for it.

redpriest's car shut off at the track causing a spin.

In this thread it shows how to repair the cable issue behind the glove box if you do not fall under the list of recalled vehicles.

http://www.m3post.com/forums/showthread.php?t=1357407


This link below is the diagnosis of the issue. Read through the posts and see if you have the same symptoms.
http://www.m3post.com/forums/showthread.php?t=1356590