E92 M3 Reduced Engine Power

[zhengf365]

The half engine light occurs while idling(I stop the car waiting for red lights or something, like 10s later the light comes out, always) with reduced engine power message.

Code:

278D BSD, Alternator Missing

279A DME Oil sensor

27E4 DME

Is the problem related to the alternator? or the regulator? or something went wrong with the cable?

[InnerBlueSkies]

Id start with the alternator, the regulator is integrated...my guess is the latter two are associated with limp mode (as a result of going into limp mode).

My recommendations assume either you or a mechanic have attempted to test the alternator. I did mine via the dash. If you go that route, a new unit is about $225 rock auto.

[bmwpower603]

You need an alternator.

Do not purchase it from rock auto.

The alternator is one of the most integral parts on a bmw. Using an aftermarket one, can cause more problems than you already have.

[InnerBlueSkies]

Originally Posted by bmwpower603

You need an alternator.

Do not purchase it from rock auto.

The alternator is one of the most integral parts on a bmw. Using an aftermarket one, can cause more problems than you already have.

This guy is an misinformed. The alternator I purchased is a Valeo, its the exact same unit that BMW uses for $400 less.

[Redd]

I bought an OEM alternator once. It wouldn't work properly, kept getting increased battery discharge errors after install. Changed it to an original BMW alt and have had zero issues since then.

So it appears OEM alts may be a bit of a hit or miss affair.