BMW E38 alternator and charging voltage
Why does the E38 charging light come on or flicker?
The most common cause is the alternator voltage regulator or worn brushes. After replacing the regulator and brush pack, the voltage at idle rose to about 14.0-14.2 V. In practice the regulator is replaced together with the brushes as one part.
What else can cause a low charging voltage?
A poor engine ground cable can drop the charging voltage even if the alternator is new. The charging light can also come on because of a blown engine management fuse or a short circuit in the oil level sensor connector. It is worth measuring the condition of a warranty alternator too.
Does any alternator fit the E38?
No. For example, the 750 needs a water-cooled 150 A alternator with part number 12317508286; an air-cooled one does not fit. The M62B44 alternator is a conventional one with brushes, and the water-cooled brushless alternator is in the M62TUB44.
What should you note when replacing the alternator?
The alternator is removed after disconnecting the battery terminals, the belt and tensioner, and removing the undertrays and the ventilation pipe, and it comes out from the front and the top. The original Bosch regulator 1 197 311 506 has been superseded by number 1 197 311 545.