12 31 009 Checking alternator and regulator switch

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.

Fig 1: Replacing Alternator Regulator Switch

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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 Signal Waveform (1 Of 7)

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Oscillogram for a faulty alternator: 

One phase interrupted.

Repair/exchange alternator.

Fig 3: Identifying Signal Waveform (2 Of 7)

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Interturn fault.

Repair/exchange alternator.

Fig 4: Identifying Signal Waveform (3 Of 7)

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Open circuit in negative diode.

Repair/exchange alternator.

Fig 5: Identifying Signal Waveform (4 Of 7)

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Short circuit in positive diode.

Repair/exchange alternator.

Fig 6: Identifying Signal Waveform (5 Of 7)

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Open circuit in positive diode.

Repair/exchange alternator.

Fig 7: Identifying Signal Waveform (6 Of 7)

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Open circuit in exciter diode.

Repair/exchange alternator.

Fig 8: Identifying Signal Waveform (7 Of 7)

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