12 31 009 Checking alternator and regulator switch

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 BMW 540i, 2002 BMW 540i, 2001 BMW 540i, 2000 BMW 540i, and 1999 BMW 540i. However, it is still accessible from the selected car via links, so may be relevant.

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.

NOTE: Minimum length of carbon brushes "A" = 5 mm.

Fig 1: Identifying Minimum Length Of Carbon Brushes

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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: Identifying Oscillogram For Fault-Free Alternator

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Oscillogram for a faulty alternator:

One phase interrupted.

Repair/exchange alternator.

Fig 3: Identifying Oscillogram For Faulty Alternator

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Interterm fault.

Repair/exchange alternator.

Fig 4: Identifying Interterm Fault

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Open circuit in negative diode.

Repair/exchange alternator.

Fig 5: Identifying Open Circuit In Negative Diode

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Short circuit in positive diode.

Repair/exchange alternator.

Fig 6: Identifying Short Circuit In Positive Diode

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Open circuit in positive diode.

Repair/exchange alternator.

Fig 7: Identifying Open Circuit In Positive Diode

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Open circuit in exciter diode.

Repair/exchange alternator.

Fig 8: Identifying Open Circuit In Exciter Diode

Courtesy of BMW OF NORTH AMERICA, INC.