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: Fault-Free Alternator Oscillogram Waveform

Courtesy of BMW OF NORTH AMERICA, INC.

Oscillogram for a faulty alternator 

One phase interrupted.

Repair/exchange alternator.

Fig 2: Faulty Alternator Oscillogram Waveform

Courtesy of BMW OF NORTH AMERICA, INC.

Interturn fault.

Repair/exchange alternator.

Fig 3: Alternator Interturn Fault Oscillogram Waveform

Courtesy of BMW OF NORTH AMERICA, INC.

Open circuit in negative diode.

Repair/exchange alternator.

Fig 4: Alternator Open Circuit In Negative Diode Oscillogram Waveform

Courtesy of BMW OF NORTH AMERICA, INC.

Short circuit in positive diode.

Repair/exchange alternator.

Fig 5: Alternator Short Circuit In Positive Diode Oscillogram Waveform

Courtesy of BMW OF NORTH AMERICA, INC.

Open circuit in positive diode.

Repair/exchange alternator.

Fig 6: Alternator Open Circuit In Positive Diode Oscillogram Waveform

Courtesy of BMW OF NORTH AMERICA, INC.

Open circuit in exciter diode.

Repair/exchange alternator.

Fig 7: Alternator Open Circuit In Exciter Diode Oscillogram Waveform

Courtesy of BMW OF NORTH AMERICA, INC.

Assemble engine.

Check function of DME/DDE.