12 31 009 Checking alternator and regulator switch

Test requirements:

Connect DIS Tester.

If charge indicator lamp is permanently lit:

Remove voltage regulator and check carbon brushes, replace if necessary.

Replace alternator regulator switch.

NOTE: Minimum length of carbon brushes "A" = 5 mm.

Fig 1: View Of Measurement "A"

Courtesy of BMW OF NORTH AMERICA, INC.

If charge indicator lamp goes out while engine is running:

Check control voltage.

Regulator switch must be replaced if control voltage is not achieved.

Replace alternator regulator switch.

From E46/E39 with multifunction regulator.

Recognizable by plug connection on regulator.

Connect DIS Tester.

Oscillogram for a fault-free alternator:

Fig 2: View Of Oscillogram For Fault-Free Alternator

Courtesy of BMW OF NORTH AMERICA, INC.

Oscillogram for a faulty alternator:

One phase interrupted.

Fig 3: View Of One Phase Interrupted

Courtesy of BMW OF NORTH AMERICA, INC.

Repair/exchange alternator.

Interturn fault.

Fig 4: View Of Interturn Fault

Courtesy of BMW OF NORTH AMERICA, INC.

Repair/exchange alternator.

Open circuit in negative diode.

Fig 5: View Of Open Circuit In Negative Diode

Courtesy of BMW OF NORTH AMERICA, INC.

Repair/exchange alternator.

Short circuit in positive diode.

Fig 6: View Of Short Circuit In Positive Diode

Courtesy of BMW OF NORTH AMERICA, INC.

Repair/exchange alternator.

Open circuit in positive diode.

Fig 7: View Of Open Circuit In Positive Diode

Courtesy of BMW OF NORTH AMERICA, INC.

Repair/exchange alternator.

Open circuit in exciter diode.

Fig 8: View Of Open Circuit In Exciter Diode

Courtesy of BMW OF NORTH AMERICA, INC.

Repair/exchange alternator.