12 31 009 Checking alternator and regulator switch

WARNING: This page is about a different variant/trim than selected.

Test requirements:

Connect DIS Tester

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.

Oscillogram for a fault-free alternator:

Fig 2: Oscillogram Pattern On Fault-Free Alternator

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Oscillogram for a faulty alternator:

One phase interrupted.

Repair/exchange alternator.

Fig 3: Oscillogram Pattern On Faulty Alternator (One Phase Interrupted)

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Interturn fault.

Repair/exchange alternator.

Fig 4: Oscillogram Pattern On Faulty Alternator (Interturn Fault)

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Open circuit in negative diode.

Repair/exchange alternator.

Fig 5: Oscillogram Pattern On Faulty Alternator (Open Circuit In Negative Diode)

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Short circuit in positive diode.

Repair/exchange alternator.

Fig 6: Oscillogram Pattern On Faulty Alternator (Short Circuit In Positive Diode)

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Open circuit in positive diode.

Repair/exchange alternator.

Fig 7: Oscillogram Pattern On Faulty Alternator (Open Circuit In Positive Diode)

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Open circuit in exciter diode.

Repair/exchange alternator.

Fig 8: Oscillogram Pattern On Faulty Alternator (Open Circuit In Exciter Diode)

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