John Deere 3020 – LCU: Unloading Auger Engage Circuit Open

The Left Control Unit (LCU) has detected an electrical anomaly in the driver circuit responsible for engaging the unloading auger. This indicates that the circuit is not completing the necessary electrical connection due to an open circuit, short circuit, over voltage, or over temperature condition (often from excessive current draw). When this fault is active, the LCU prevents the unloading auger from engaging to protect the electrical system from further damage.

• 9540 WTS
• 9560 WTS
• 9580 WTS
• 9640 WTS
• 9660 WTS
• 9680 WTS
• 9660 CTS
• 9560 STS
• 9650 STS
• 9660 STS
• 9750 STS
• 9760 STS
• 9860 STS
• 9870 STS
• S550
• S660
• S670
• S680
• S690

1. 1

   Verify permissive conditions are met (operator must be seated, road transport disconnect switch in 'field' position, and auger swung out to minimum position, e.g., 50%).

2. 2

   Inspect the wiring harness and connectors from the Left Control Unit to the unloading auger engage switch and solenoid for chafed insulation, melted wires, corroded connectors, or loose pins.

3. 3

   Check related fuses and relays in the engine compartment relay panel that supply power to the control units.

4. 4

   Check the yellow unloading auger engage switch on the control panel for failure.

5. 5

   Check the unloading auger engage solenoid for a failing coil.

1. 1

   Isolate the fault

   Disconnect the unloading auger engage solenoid from the main wiring harness. Clear the fault codes and attempt to engage the system again. If the fault code does not return, the solenoid is likely shorted or open. If the fault code does return, the problem lies upstream in the wiring or the Left Control Unit's driver circuit.

2. 2

   Test the wiring

   Using a multimeter, check for continuity on the signal wire from the LCU to the solenoid (infinite resistance indicates a broken wire). Check for a short to ground by measuring resistance from the signal wire to a known good chassis ground (low resistance indicates a short). Check for a short to power by turning the key on (engine off) and measuring voltage on the signal wire at the disconnected solenoid connector (there should be no voltage until the engage switch is pressed).

3. 3

   Test the solenoid

   If the wiring is good, measure the resistance across the two pins of the solenoid coil and compare to manufacturer specifications. An infinite reading indicates an open coil, while a very low or zero reading indicates a shorted coil.

4. 4

   Replace Left Control Unit

   If the wiring and solenoid both test as good, the fault may lie within the Left Control Unit's internal driver circuit. Replace the LCU if necessary.