John Deere HMM523107 – HMM: ServiceAlert Plunger Initialization Failure

The GREENSTAR™ moisture sensor system has detected a failure during the initialization process of the plunger. The plunger, which moves to collect a grain sample for moisture analysis, is not retracting or extending as commanded by the control system. This failure disables the moisture sensing function.

• 9450
• 9540
• 9550
• 9560 STS
• 9570 STS
• 9580
• 9640
• 9650
• 9650 STS
• 9660 STS
• 9660 WTS
• 9670
• 9670 STS
• 9680
• 9750 STS
• 9760 STS
• 9770 STS
• 9780
• 9860 STS
• 9870 STS
• 9880 STS
• C670
• T550
• T560
• T660
• T670
• W540
• W550
• W650
• W660

1. 1

   Access the moisture sensor diagnostics page on the in-cab display for detailed troubleshooting information.

2. 2

   Check for other related diagnostic trouble codes, such as 'Motor Stalled', 'Actuator Shorted', or 'Relay Failure', which can indicate the specific origin of the fault.

3. 3

   Inspect the fuse for the moisture sensor circuit and check any associated relays for failure.

4. 4

   Monitor the actuator's current draw and cycle time on the diagnostic page to determine if the motor is under excessive load.

5. 5

   Attempt to manually retract the plunger via the moisture sensor diagnostic page to test motor function and provide access for cleaning. To extend the plunger after retraction, you may need to cycle the key power.

6. 6

   Visually inspect the sensor plates and plunger area for a buildup of green plant material, weed seeds, or other debris that could cause the motor to stall. Clean thoroughly (denatured alcohol is suggested).

1. 1

   Prepare machine for service

   Shut off the engine, set the parking brake, and remove the key before performing any physical work on the moisture sensor.

2. 2

   Access the moisture sensor

   Locate the moisture sensor in the clean grain tank. Access may require folding down the loading auger.

3. 3

   Clean the sensor assembly

   Using the diagnostic menu, retract the plunger. Thoroughly clean the moisture sensor plates and the area around the plunger to remove any obstructions (denatured alcohol is suggested). After cleaning, cycle the power to see if the plunger initializes correctly.

4. 4

   Inspect and replace components

   If cleaning fails to resolve the initialization issue, remove the moisture sensor unit from the machine (the entire unit is held by a few bolts and can be removed for service on a workbench). Disassemble the unit to check for worn plastic parts or a deteriorated rubber seal on the plunger. Replace the faulty component (actuator motor, circuit board, or entire moisture sensor module) as needed.

5. 5

   Reassemble and calibrate

   Install the repaired or new moisture sensor assembly. Navigate to the moisture sensor calibration menu on the display. Ensure the engine is off and the sensor is empty of grain, then follow the on-screen prompts to start the automatic calibration process.