John Deere 3108 – RCU: Spreader Speed 1 High Side Open Circuit

The Rear Control Unit (RCU) has detected a break or open circuit in the high-side of the electrical circuit (cc# 343) responsible for controlling the speed of spreader number 1. This open circuit prevents electrical current from completing its path, which stops the proper operation of the spreader component. This could be due to a disconnected connector, a broken wire, or a faulty component within the circuit.

• 9560 STS
• 9570 STS
• 9650 STS
• 9660 STS
• 9670 STS
• 9750 STS
• 9760 STS
• 9770 STS
• 9860 STS
• 9870 STS
• S540
• S550
• S650
• S660
• S670
• S680
• S690
• S760
• S770
• S780
• S790

1. 1

   Visually inspect the wiring harness and connectors associated with the spreader speed sensor and the RCU. Look for any visible signs of damage, such as frayed or broken wires, and ensure all connectors are fully seated and free of corrosion.

2. 2

   Check for disconnected components; a 'Motor Open Circuit' message can be displayed when a motor is disconnected. Verify that all harnesses are correctly installed.

3. 3

   Inspect fuses related to the RCU and relevant electrical systems (e.g., fuse F53 for RCU Power 1 on a 9870 STS).

4. 4

   If a low shaft speed is indicated, check for broken or disconnected sensor wires and a damaged sensor.

1. 1

   Shut down and secure machine

   Shut off the engine, set the parking brake, and remove the key to prevent accidental starting before beginning any work.

2. 2

   Locate components

   Identify the location of the RCU and the spreader speed sensor on the spreader assembly. Accessing the spreader may require raising it and removing spreader disks.

3. 3

   Test circuit continuity

   Using a multimeter, test for continuity along the wire for circuit cc# 343 between the RCU and the spreader speed sensor connector. A lack of continuity confirms an open circuit in the wiring.

4. 4

   Repair or replace wiring

   If a break in the wire is found, repair it using appropriate connectors and heat shrink for a weather-resistant connection. If the harness is extensively damaged, replace it.

5. 5

   Test the sensor

   If the wiring is intact, the sensor itself may be faulty. Following technical manual guidance, short the sensor wires to ground to see if the fault clears, which indicates a faulty sensor.

6. 6

   Replace the sensor

   If the sensor is determined to be the cause, replace it. Ensure the air gap between the new sensor and the target wheel is set to the manufacturer's specification (e.g., 1 mm or 1/16 in. for some chopper speed sensors).

7. 7

   Clear codes and test

   After the repair is complete, clear the diagnostic trouble codes and operate the spreader to ensure the fault does not return.