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: Identifying Minimum Carbon Brush Length

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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: Fault-Free Alternator Oscillogram

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Oscillogram for a faulty alternator: 

One phase interrupted.

Repair/exchange alternator.

Fig 3: Faulty Alternator Oscillogram

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Interturn fault.

Repair/exchange alternator.

Fig 4: Alternator Oscillogram - Interturn Fault

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Open circuit in negative diode.

Repair/exchange alternator.

Fig 5: Alternator Oscillogram - Open Circuit In Negative Diode

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Short circuit in positive diode.

Repair/exchange alternator.

Fig 6: Alternator Oscillogram - Short Circuit In Positive Diode

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Open circuit in positive diode.

Repair/exchange alternator.

Fig 7: Alternator Oscillogram - Open Circuit In Positive Diode

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Open circuit in exciter diode.

Repair/exchange alternator.

Fig 8: Alternator Oscillogram - Open Circuit In Exciter Diode

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