John Deere 3353.14 – BCU (Basic Control Unit) or RCU (Rear Control Unit): Alternator Malfunction (Alternator Field is Off When Commanded On)

The controller detects that the 'Alternator Field is Off When Commanded On'. This means the control unit has sent the excitation signal to turn the alternator on and generate power, but the alternator is failing to produce a charge. The symptom 'Over Heating, Turn Off Some Lights' is a secondary warning generated by the system to shed electrical load because the machine is running solely on battery reserve power.

• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 6230
• 6330
• 6430
• 7130
• 7230
• 7330
• 7430
• 7530
• 9470 STS
• 9570 STS
• 9670 STS
• 9770 STS
• 9870 STS

1. 1

   Battery Voltage Test: With the engine off, check the battery voltage (should be ~12.6V). Start the engine and check again; if the alternator is working, it should read between 13.5V and 14.5V. If it remains at or drops below 12.6V, the alternator is not charging.

2. 2

   Belt Inspection: Inspect the serpentine/alternator drive belt. A loose, glazed, or snapped belt will prevent the alternator pulley from spinning at the correct speed.

3. 3

   Wiring and Connections: Inspect the wiring harness at the rear of the alternator. Check the B+ (main power) and L (excitation/lamp) terminals. Look for loose nuts, broken wires, or heavy corrosion.

4. 4

   Controller Output Check: Verify that the BCU/RCU is actually sending the 12V wake-up/excitation signal to the alternator when the key is turned on. If the signal is missing, the issue is in the wiring harness or the controller, not the alternator itself.

1. 1

   Disconnect Power

   Turn off the ignition, remove the key, and disconnect the negative (-) battery cable to prevent electrical shorts.

2. 2

   Remove the Belt

   Use a breaker bar or wrench to release the tension on the drive belt tensioner. Slip the belt off the alternator pulley.

3. 3

   Disconnect Wiring

   Remove the rubber boots covering the alternator terminals. Unbolt the heavy gauge B+ wire and unplug the voltage regulator/excitation connector.

4. 4

   Remove the Alternator

   Remove the upper and lower mounting bolts securing the alternator to the engine bracket. Carefully extract the heavy alternator from the engine bay.

5. 5

   Install the New Alternator

   Position the new alternator into the bracket and hand-tighten the mounting bolts. Torque the bolts to OEM specifications.

6. 6

   Reconnect Wiring

   Reattach the electrical connections, ensuring the B+ terminal nut is tight and the plug is fully seated.

7. 7

   Reinstall the Belt

   Route the drive belt back over the pulleys, release the tensioner to apply tension, and ensure the belt is seated properly in all pulley grooves.

8. 8

   Test

   Reconnect the negative battery cable. Start the engine and use a multimeter to verify the charging voltage is now 13.5V–14.5V. Clear the 003353.14 code via the cab monitor.