John Deere 3353.09 – ECU / RCU: Alternator Fault / Alternator Excitation Error

The control software has detected that the alternator is not being driven effectively, the alternator field circuit is malfunctioning (e.g., open circuit or off when commanded on), or the system is failing to charge. As a protective reaction, the machine's software may reduce or limit certain functions to conserve battery power.

• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 9570 STS
• 9670 STS
• 9770 STS
• 9870 STS
• PowerTech 4.5L
• PowerTech 6.8L
• PowerTech 8.1L

1. 1

   Inspect the alternator drive belt (fan belt) for excessive wear, glazing, looseness, or breakage (a slipping belt is a primary cause)

2. 2

   Test alternator output voltage at the output terminal while the engine is running (should be 13.5V–14.5V for a 12V system, or 27V–28V for a 24V system)

3. 3

   Inspect the alternator field circuit (circuit #007) for open circuits, shorts to ground, or corroded connectors

4. 4

   Perform a battery load test to ensure the batteries are in good condition and capable of holding a charge (a dead cell can overload the alternator)

1. 1

   Disconnect Power

   Disconnect the negative battery cable(s) to prevent electrical shorts.

2. 2

   Belt Replacement (If Applicable)

   If the diagnostic checks revealed a worn or broken drive belt, use a breaker bar to relieve tension on the automatic belt tensioner and install a new OEM poly-rib belt.

3. 3

   Alternator Replacement (If Applicable)

   Disconnect the wiring harness and the main output cable from the rear of the alternator. Remove the mounting bolts securing the alternator to the engine bracket. Install the new alternator and torque the mounting bolts to OEM specifications. Reconnect the wiring harness and output cable, ensuring the connections are clean and tight.

4. 4

   Wiring Repair

   If the alternator tested fine but the field circuit was open, locate the break in the wiring harness between the alternator and the ECU/RCU and repair it using weather-sealed splices.

5. 5

   System Reset

   Reconnect the battery. Turn the key to the ON position, clear the stored ECU/RCU fault codes via the cab monitor or diagnostic tool, and start the engine to verify the charging voltage has returned to normal.