Alternator or Voltage Regulator?

TreyBinkley · 08-22-2023, 08:55 PM

Desperately trying to diagnose an electrical gremlin causing random lim mode, dcs, and dbc errors.

Sometimes it drives fine and sometimes it doesn't.

Brand new battery and registered.

Any way to tell which is the problem?

I'm pulling 12.5v when not running and 13.9-14v when running.

TreyBinkley · 08-22-2023, 09:27 PM

To add this voltage measurements are from the dash. I am measuring 14.6v at 2k rpms at the alternator. The car had issues with runnability and those codes. Replaced the battery and now said issues have resurfaced after 50 miles of smooth driving. Trying to leave for a trip in 2 days and desperately trying to find a solution. Can't seem to reason if it's the alternator or the regulator or just some hidden codes I missed clearing.

Please Help

mainbearing · 08-23-2023, 11:28 AM

I some over-voltage codes and cylinder #6 misfires in INPA. That was when I replaced the voltage regulator (Bosch 180 amp alt) per VehicularDIY's video and other threads on this forum.

If it was a voltage regulator problem, an INPA scan should tell you some problem codes.

Maybe start with cable connections? Maybe there are some less than perfect connections causing your problems?

BRG_N54 · 08-23-2023, 11:39 AM

My personal experience with a bad voltage regulator did not cause half engine error. Only after it had overheated due to the water pump not running did it reduce power, but I also got the overheat warning.

It sounds like your voltages are in the proper range, but the alternator has other failure modes. The diodes can go bad and the clutch in the pully can go bad. I know there are many issues reported with the grounding straps that are all over the car. You didn't mention any vehicle specs, so it might help us to help you if you give a bit more information about the car, model, mileage, etc.

lordnikon · 08-23-2023, 02:07 PM

Your voltages looks fine.

TreyBinkley · 08-28-2023, 04:22 PM

Had that happened with a voltage regulator last year.

Current stats:
2009 E90 Manual 195k on the clock and has been super good for me since I bought it at 150k.
New Battery, 1 year old voltage regulator, Voltages seem fine, when battery was replaced I used Bav Tech to reset battery and all used JB4 to reset adaptations and did the 30 second throttle reset.

Currently the car runs but is in limp mode. Has a smooth idle though. Throwing the following errors:
Brake Light
DBC Off
DSC Off
Engine Limp mode
Slow Start but always starts

I can check ground strap, Is there anything else to do or check?

08-22-2023, 08:55 PM	#1
TreyBinkley New Member 0 Rep 17 Posts Drives: Bmw 335i Join Date: Jan 2020 Location: Chambersburg PA iTrader: (0)	Alternator or Voltage Regulator? Desperately trying to diagnose an electrical gremlin causing random lim mode, dcs, and dbc errors. Sometimes it drives fine and sometimes it doesn't. Brand new battery and registered. Any way to tell which is the problem? I'm pulling 12.5v when not running and 13.9-14v when running.
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08-22-2023, 09:27 PM	#2
TreyBinkley New Member 0 Rep 17 Posts Drives: Bmw 335i Join Date: Jan 2020 Location: Chambersburg PA iTrader: (0)	To add this voltage measurements are from the dash. I am measuring 14.6v at 2k rpms at the alternator. The car had issues with runnability and those codes. Replaced the battery and now said issues have resurfaced after 50 miles of smooth driving. Trying to leave for a trip in 2 days and desperately trying to find a solution. Can't seem to reason if it's the alternator or the regulator or just some hidden codes I missed clearing. Please Help
	Appreciate 0 Quote

08-23-2023, 11:28 AM	#3
mainbearing Lieutenant Colonel 1085 Rep 1,682 Posts Drives: BMW 328i Join Date: Apr 2019 Location: LA iTrader: (0)	I some over-voltage codes and cylinder #6 misfires in INPA. That was when I replaced the voltage regulator (Bosch 180 amp alt) per VehicularDIY's video and other threads on this forum. If it was a voltage regulator problem, an INPA scan should tell you some problem codes. Maybe start with cable connections? Maybe there are some less than perfect connections causing your problems?
	Appreciate 0 Quote

08-23-2023, 11:39 AM	#4
BRG_N54 Second Lieutenant 307 Rep 263 Posts Drives: Green '07 & Arctic '08 335i's Join Date: Jan 2023 Location: Monterey Peninsula iTrader: (0) Garage List 2008 BMW 335i [0.00] 2007 BMW 335i [0.00]	Ground strap? My personal experience with a bad voltage regulator did not cause half engine error. Only after it had overheated due to the water pump not running did it reduce power, but I also got the overheat warning. It sounds like your voltages are in the proper range, but the alternator has other failure modes. The diodes can go bad and the clutch in the pully can go bad. I know there are many issues reported with the grounding straps that are all over the car. You didn't mention any vehicle specs, so it might help us to help you if you give a bit more information about the car, model, mileage, etc.
	Appreciate 0 Quote

08-23-2023, 02:07 PM	#5
lordnikon Lieutenant 382 Rep 470 Posts Drives: Break My Wallet Join Date: Feb 2023 Location: Ontario iTrader: (0) Garage List 2011 BMW 328i xDrive [0.00]	Your voltages looks fine.
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08-28-2023, 04:22 PM	#6
TreyBinkley New Member 0 Rep 17 Posts Drives: Bmw 335i Join Date: Jan 2020 Location: Chambersburg PA iTrader: (0)	Had that happened with a voltage regulator last year. Current stats: 2009 E90 Manual 195k on the clock and has been super good for me since I bought it at 150k. New Battery, 1 year old voltage regulator, Voltages seem fine, when battery was replaced I used Bav Tech to reset battery and all used JB4 to reset adaptations and did the 30 second throttle reset. Currently the car runs but is in limp mode. Has a smooth idle though. Throwing the following errors: Brake Light DBC Off DSC Off Engine Limp mode Slow Start but always starts I can check ground strap, Is there anything else to do or check?
	Appreciate 0 Quote