John Deere 3108 – RCU (Control Unit RCU and Right Power Module): Spreader Speed 1 High Side Not Activating as Commanded

The Right Power Module / Control Unit (RCU) has commanded the spreader speed 1 high side circuit to turn ON, but the system has not detected its activation. The system does not detect a specific electrical fault such as an open or short circuit, indicating an issue with the physical execution of the command (such as a failing actuator or mechanical binding) or an internal RCU fault rather than a simple wiring failure.

• 9570 STS
• 9670 STS
• 9770 STS
• 9870 STS
• S660
• S670
• S670H
• S680
• S680H
• S685
• S685H
• S690
• S690H
• S760
• S770
• S780
• S785
• S790

1. 1

   Carefully inspect the wiring harness leading to the spreader speed actuator for any signs of damage, such as chafed or frayed wires, loose connections, or corrosion.

2. 2

   With the spreader commanded ON, use a multimeter to check for voltage at the actuator's electrical connector. The absence of voltage indicates a problem upstream in the wiring or the RCU.

3. 3

   Check for any blown fuses or faulty relays that supply power to the RCU or the spreader circuit.

4. 4

   If voltage is present at the connector but the actuator does not function, attempt to power the actuator directly with a 12V source to confirm its mechanical failure.

1. 1

   Isolate the fault

   Perform the diagnostic checks to confirm whether the fault lies with the wiring, connectors, or the actuator itself.

2. 2

   Repair wiring

   If a wiring issue is found, repair the damaged section or replace the harness if necessary. Ensure all connections are clean and secure.

3. 3

   Replace the actuator

   If the actuator is determined to be faulty, disconnect the electrical connector from the old actuator, remove the mounting hardware, and install the new Advanced PowerCast™ Actuator. Ensure it is correctly oriented and securely fastened, then reconnect the electrical connector.

4. 4

   Clear codes and test

   After the repair, clear the fault codes from the RCU and operate the spreader to verify that the issue is resolved and the code does not reappear.