John Deere 1498 – ACU or LC1: Header Engage Output Transistor Fault

The header engage output transistor, an internal component of the control module, has detected an open circuit, short circuit, over-voltage, or over-temperature condition. Upon detecting this fault, the Armrest Control Unit (ACU) immediately disengages power to the header circuit to prevent further system damage. The header cannot be re-engaged until the fault condition is resolved.

• 9470 STS
• 9560 STS
• 9570 STS
• 9650 STS
• 9660 STS
• 9670 STS
• 9750 STS
• 9760 STS
• 9770 STS
• 9860 STS
• 9870 STS
• 9880 STS
• 9540
• 9580
• 9640
• 9660
• 9680
• CTS
• C670
• T550
• T560
• T660
• T670
• W540
• W550
• W650
• W660
• 7760

1. 1

   Verify operator and safety switch function: ensure the operator is seated squarely in the seat, check that the road transport disconnect switch is in the 'field' position, and verify the main header engage switch is functioning correctly

2. 2

   Visually inspect the wiring harness leading to the electromagnetic header clutch for any signs of damage, such as chafing, breaks, or corrosion on the connectors

3. 3

   Inspect the electromagnetic header clutch: check the wires connected directly to the clutch for integrity, inspect the internal brushes (worn or stuck brushes can cause an open circuit), and check the air gap

4. 4

   Inspect any relays associated with the header engagement circuit

5. 5

   Perform a circuit load test: Do not simply check for voltage at the unplugged connector. Disconnect the harness from the electric clutch, connect a test light in its place, and attempt to engage the header. If the light illuminates, the control unit, wiring, and switches are likely functioning correctly, pointing to a faulty clutch

6. 6

   Check for other active diagnostic codes, such as CAN bus communication errors or other sensor failures that can sometimes be related

1. 1

   Repair Wiring

   If damaged wiring is found, repair the affected section using sealed connectors and appropriate gauge wire.

2. 2

   Clean Connections

   If corrosion is present on any connectors, disconnect them and clean the terminals thoroughly.

3. 3

   Replace Electric Clutch

   If the diagnostic tests point to a failure in the electromagnetic clutch (e.g., open coil, worn brushes), the clutch assembly must be replaced.

4. 4

   Disconnect Battery

   Before starting any work on the control unit, disconnect the machine's battery.

5. 5

   Access the ACU

   The Armrest Control Unit is located within the armrest console. Access may require removing panels or the seat.

6. 6

   Label and Disconnect

   Carefully label and disconnect all electrical connectors from the old control unit.

7. 7

   Remove and Replace

   Unbolt and remove the old ACU. Install the new unit in its place.

8. 8

   Reconnect and Reassemble

   Reconnect all electrical connectors to the new ACU, ensuring each is seated correctly. Reassemble the armrest console and any other components that were removed.

9. 9

   Reconnect Battery and Test

   Reconnect the battery and turn the key to the 'ON' position. Clear all fault codes. Start the machine and test the header engagement function to confirm the repair.