DME code 278D: BSD/Alternator

MikeHawk7 · 03-06-2026, 09:38 PM

I'm trying to diagnose this before jumping into the engine bay and digging into the alternator.

If the BSD wire is disconnected, is this a code that pops up immediately or does it take some time to show itself? My code doesn't show up right away after resetting codes.

I'm expecting this could turn into an alternator replacement, but if it's simply a disconnected wire that would be ideal.

Multimeter shows 14.6 volts at idle. If it's just a voltage regulator issue I'm going to replace the alternator instead since I'm already in there for the peace of mind.

tsk94 · 03-12-2026, 04:46 PM

I had the same code on my own car the other summer. It came along with many other drivability issues of the car stalling/dying.
It ended up being the main engine ground, the one near the oil pan, was slightly loose. I ended up replacing that ground strap with a new OEM piece and making sure it was properly torqued down. After that, I never had the issue again.

I started by replacing the battery, then the alternator, and neither helped. The ground strap was the culprit the whole time. I'd suggest starting there. Along with the ground on the top of the valve cover.

03-06-2026, 09:38 PM	#1
MikeHawk7 Second Lieutenant 152 Rep 206 Posts Drives: 2013 M3: E92, ZCP, DCT Join Date: Aug 2017 Location: San Diego, CA iTrader: (5) Garage List 2003 BMW 530i [0.00] 2013 BMW M3 [0.00]	DME code 278D: BSD/Alternator I'm trying to diagnose this before jumping into the engine bay and digging into the alternator. If the BSD wire is disconnected, is this a code that pops up immediately or does it take some time to show itself? My code doesn't show up right away after resetting codes. I'm expecting this could turn into an alternator replacement, but if it's simply a disconnected wire that would be ideal. Multimeter shows 14.6 volts at idle. If it's just a voltage regulator issue I'm going to replace the alternator instead since I'm already in there for the peace of mind. __________________ -Mike M. 2013 M3 [E92, Alpine White, ZCP, DCT] 2003 530i Last edited by MikeHawk7; 03-06-2026 at 09:43 PM..
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03-12-2026, 04:46 PM	#2
tsk94 Lieutenant Colonel 1727 Rep 1,716 Posts Drives: E92 M3, E82 128i, F82 M4, E36 Join Date: May 2017 Location: Calgary iTrader: (2)	I had the same code on my own car the other summer. It came along with many other drivability issues of the car stalling/dying. It ended up being the main engine ground, the one near the oil pan, was slightly loose. I ended up replacing that ground strap with a new OEM piece and making sure it was properly torqued down. After that, I never had the issue again. I started by replacing the battery, then the alternator, and neither helped. The ground strap was the culprit the whole time. I'd suggest starting there. Along with the ground on the top of the valve cover.
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