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.

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 Waveform 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 Waveform For Faulty Alternator

Courtesy of BMW OF NORTH AMERICA, INC.

Inter turn fault.

Repair/exchange alternator.

Fig 3: Oscillogram Waveform For Inter Turn Fault

Courtesy of BMW OF NORTH AMERICA, INC.

Open circuit in negative diode.

Repair/exchange alternator.

Fig 4: Oscillogram Waveform For Open Circuit In Negative Diode

Courtesy of BMW OF NORTH AMERICA, INC.

Short circuit in positive diode.

Repair/exchange alternator.

Fig 5: Oscillogram Waveform For Short Circuit In Positive Diode

Courtesy of BMW OF NORTH AMERICA, INC.

Open circuit in positive diode.

Repair/exchange alternator.

Fig 6: Oscillogram Waveform For Open Circuit In Positive Diode

Courtesy of BMW OF NORTH AMERICA, INC.

Open circuit in exciter diode.

Repair/exchange alternator.

Fig 7: Oscillogram Waveform For Open Circuit In Exciter Diode

Courtesy of BMW OF NORTH AMERICA, INC.

Assemble engine.

Check function of DME/DDE.