John Deere 1490 – Armrest Control Unit: Backshaft Speed Unknown

The Armrest Control Unit is not receiving a signal from the magnetic pickup sensor that monitors the rotational speed of the feeder house backshaft. This is a critical safety and operational input, as the system needs to confirm the backshaft has stopped rotating before allowing the feeder house reverser to engage. If the reverser is engaged while the feeder house is in motion, it can lead to significant mechanical damage.

• 9560
• 9660
• 9760
• 9860
• 9670
• 9770
• 6620
• 7720
• 8820
• CTS
• 9400
• 9500
• 9600
• 9470 STS
• 9570 STS
• S550
• S660
• S670
• S560
• S690
• 9870 STS

1. 1

   With the engine off and the key removed, visually inspect the backshaft speed sensor and sensor wheel on the lower right-hand side of the feeder house for a loose wheel or debris buildup.

2. 2

   Examine the wiring harness and connectors for damage, chafing, breaks, or corrosion, and disconnect and reconnect the electrical connectors for the sensor and the Armrest Control Unit to ensure a secure connection.

3. 3

   Check the sensor air gap between the sensor and the sensor wheel (specification is typically 1 mm or 1/16 in.).

4. 4

   Perform a basic electrical test by disconnecting the sensor, connecting a voltmeter, and spinning the shaft by hand to check for a small AC voltage.

5. 5

   Perform a circuit test by shorting the sensor wires to ground; if the warning light and buzzer turn off, the sensor is faulty. If the fault persists, check the wiring or control unit.

1. 1

   Ensure safety and access sensor

   Shut off the combine engine, set the parking brake, remove the key, and remove protective shields to access the sensor on the lower right side of the feeder house.

2. 2

   Secure sensor wheel

   If the sensor wheel is loose, loosen the set screw, reposition the wheel correctly on the shaft, and securely tighten the set screw. Consider adding a bearing collar to keep the wheel in place.

3. 3

   Repair wiring

   If wiring damage was found during diagnostics, repair the affected wires or replace the wiring harness.

4. 4

   Replace faulty sensor

   If the sensor failed electrical testing, unscrew and remove the old sensor. Install the new sensor, ensuring it is threaded in correctly, set the air gap to 1 mm (1/16 in.), and connect the wiring harness.

5. 5

   Reassemble and verify

   Reinstall any removed shields, start the combine, clear the fault codes, engage the separator, and observe the backshaft speed on the display to confirm the repair.