John Deere HMM522878 – HMM: Moisture Sensor Over Temperature

A Service Alert indicating that the moisture sensor has exceeded its normal operating temperature threshold of 85°C (185°F). The moisture sensor will cease to function when its temperature rises above this limit. This alert signals an operational issue that requires prompt attention to prevent inaccurate readings, escalation of the fault, or potential machine damage.

• 9560 STS
• 9570 STS
• 9660 STS
• 9670 STS
• 9760 STS
• 9770 STS
• 9870 STS
• S600
• S700
• T-Series
• W-Series

1. 1

   Verify if the fault is active by shutting down and restarting the machine

2. 2

   Allow the machine and moisture sensor time to cool down

3. 3

   Inspect the moisture sensor plates for buildup of green plant sap, weed seeds, or other debris

4. 4

   Check for obstructions around the moisture sensor that could restrict airflow or stall the actuator

5. 5

   Inspect the moisture sensor wiring harness and connectors for damage or corrosion

6. 6

   Review moisture sensor diagnostics on the display (check grain temperature and actuator current)

1. 1

   Allow sensor to cool

   Stop the machine and allow sufficient time for the moisture sensor to cool below its 85°C (185°F) threshold.

2. 2

   Clean the moisture sensor

   Shut off the engine, set the parking brake, and remove the key. Access the sensor in the clean grain elevator or grain tank area. Gently clean buildup from the sensor plates using a soft cloth and mild glass cleaner. Do not use abrasive materials.

3. 3

   Calibrate sensor temperature

   At the beginning of the day (before machine heat affects the sensor), navigate to the calibrations menu on the display. Select 'Moisture Sensor Temperature Calibration', compare the displayed temperature to the actual ambient temperature, and adjust the display to match.

4. 4

   Perform moisture calibration

   With the engine off and the moisture sensor empty, perform a full moisture calibration if readings remain inaccurate.

5. 5

   Replace internal components

   If the fault persists, internal relays within the moisture sensor module may have failed. Replace the circuit board or the entire moisture sensor module as required.