Case IH 520588-05 - BCM – Body Control Module (BCM): Alternator Control Circuit / Alternator Excitation Driver - Current Below Normal or Open Circuit

The Alternator Control Circuit or Alternator Excitation Driver is experiencing 'Current Below Normal or Open Circuit'. The excitation circuit provides the initial voltage to the alternator's field windings to begin the charging process. An open circuit means infinite resistance, a broken connection, or zero voltage, which prevents the alternator from charging the battery.

• MAGNUM AFS Connect
• Axial-Flow Combines (2577, 2588)
• Magnum
• Steiger
• Maxxum
• Farmall
• WD2303 Windrower

1. 1

   Verify the active DTC and record any related freeze-frame data using a diagnostic scan tool

2. 2

   Visually inspect the alternator's excitation terminal (often labeled as the L-terminal, D+, or IGN), the connector, and the wiring harness for physical damage, corrosion, loose pins, or burnt insulation

3. 3

   Check the electrical fuses associated with the alternator excitation circuit (e.g., 20-amp fuse labeled 'Alternator Excitation/Ether Start')

4. 4

   Disconnect the harness and perform a continuity test between the alternator excitation terminal and the BCM output pin to check for high or infinite resistance

5. 5

   With the ignition ON and the engine OFF, backprobe the excitation terminal to verify if it is receiving the expected voltage signal from the BCM

6. 6

   Check the alternator's internal field coil for an open circuit

1. 1

   Disconnect Power

   Always disconnect the negative (-) battery cable before performing electrical repairs to prevent sparks or module damage.

2. 2

   Replace Fuses

   If the excitation fuse is blown, replace it. Ensure you also trace the circuit to repair any short-to-ground conditions that may have caused the fuse to blow.

3. 3

   Repair Wiring

   Repair any broken wires, loose contacts, or chafed harness sections between the BCM and the alternator excitation terminal.

4. 4

   Replace Alternator

   If the wiring harness and BCM output are verified to be functioning properly, but the alternator's internal field winding is open, remove and replace the alternator assembly.

5. 5

   Reassemble and Test

   Reconnect the negative battery cable, start the engine, and verify with a multimeter that the alternator is outputting the correct charging voltage to the battery.

6. 6

   Clear Codes

   Clear the fault codes from the BCM using a diagnostic scan tool.