12 31 009 Checking alternator (BSD)

Necessary preliminary tasks: 

• Correct connections on charged battery
• Correct connections on alternator and starter motor
• Good ground connection between engine and body
• Tensioned ribbed V-belt
• Read out DME/DDE fault memory.

The alternator is not connected to the charge telltale light.

The alternator can identify various faults.

BSD alternator can be recognized by the plug connection on the alternator.

Connect diagnosis tester.

• Function selection
• Complete vehicle
• Drive
• Voltage and current regulation
• Voltage and current generation
• Alternator
• Follow instruction in diagnostic program

Oscillogram for a fault-free alternator: 

Fig 1: Oscillogram Graph For Fault-Free Alternator

Courtesy of BMW OF NORTH AMERICA, INC.

Oscillogram for a faulty alternator: 

One phase interrupted.

Repair/exchange alternator.

Fig 2: Oscillogram Graph For Faulty Alternator

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Interturn fault.

Repair/exchange alternator.

Fig 3: Identifying Interturn Fault

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Open circuit in negative diode.

Repair/exchange alternator.

Fig 4: Identifying Open Circuit In Negative Diode

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Short circuit in positive diode.

Repair/exchange alternator.

Fig 5: Identifying Short Circuit In Positive Diode

Courtesy of BMW OF NORTH AMERICA, INC.

Open circuit in positive diode.

Repair/exchange alternator.

Fig 6: Identifying Open Circuit In Positive Diode

Courtesy of BMW OF NORTH AMERICA, INC.

Open circuit in exciter diode.

Repair/exchange alternator.

Fig 7: Identifying Open Circuit In Exciter Diode

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Assemble engine.

Check function of DME/DDE.