12 31 009 Checking alternator and regulator switch

Test requirements: 

• Correct connections on charged battery
• Correct connections on alternator and starter motor
• Good ground connection between engine and body
• Tightened drive belt

Connect DIS Tester. 

• Measurement
• Checking alternator

If charge indicator lamp is permanently lit:

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

Replace alternator regulator switch.

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.

• Function selection
• Complete vehicle
• Drive

• Voltage and current regulation
• Voltage and current generation
• Work through test modules

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

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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.