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.

NOTE: The alternator with BSD interface can communicate with the engine control unit (DME/DDE).

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

G04740394

Courtesy of BMW OF NORTH AMERICA, INC.

Oscillogram for a faulty alternator

One phase interrupted.

Repair/exchange alternator.

Fig 2: Faulty Alternator Oscillogram Waveform

G04740395

Courtesy of BMW OF NORTH AMERICA, INC.

Interturn fault.

Repair/exchange alternator.

Fig 3: Alternator Interturn Fault Oscillogram Waveform

G04740396

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

G04740397

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

G04740398

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

G04740399

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

G04740400

Courtesy of BMW OF NORTH AMERICA, INC.

Assemble engine.

Check function of DME/DDE.