Fendt 18.2.05 – MFA (Multifunction Armrest - A039 or A100) / Basic Control Unit ECU (A050): S053 - Switch, driver seat

Fault code 18.2.05 indicates that the driver seat is not "loaded" (the seat switch does not detect the operator's weight) when the automated steering system (Auto-Guide / VarioGuide) is activated. This is a safety interlock designed to ensure the operator is physically present in the seat before the tractor is allowed to steer itself.

• 922 Vario COM III
• 924 Vario COM III
• 927 Vario COM III
• 930 Vario COM III
• 933 Vario COM III
• 936 Vario COM III
• 300 Vario
• 400 Vario COM III
• 700 Vario COM III / SCR
• 800 Vario COM III / 820 Vario greentec
• 900 Vario COM III / SCR

1. 1

   Verify Operator Presence: Ensure the driver is fully seated and the seat cushion is compressing properly when attempting to activate the steering system.

2. 2

   Inspect for Obstructions: Check for tools, debris, or equipment wedged behind or under the seat suspension. Obstructions can prevent the seat from traveling downward far enough to engage the switch.

3. 3

   Check Seat Adjustment: Ensure the seat suspension (especially on air-ride models) is adjusted correctly for the driver's weight. If the suspension is too stiff, a lighter operator may not trigger the switch.

4. 4

   Inspect Wiring: Check the wiring harness and connector leading to the seat switch (S053) under the seat for moisture, corrosion, or broken wires.

5. 5

   Test the Switch: Use a multimeter to test the seat switch for proper continuity when weight is applied to the seat cushion.

1. 1

   Park the tractor on a level surface, turn off the engine, and remove the key.

   Ensure the machine is safely parked before beginning inspection.

2. 2

   Inspect the area under the seat and clear any debris or obstructions.

   Remove any items that might prevent the seat from traveling downward.

3. 3

   Locate the seat switch (S053) under the seat cushion.

   If the switch is determined to be faulty, locate it under the seat cushion (Fendt primarily uses Grammer seats).

4. 4

   Disconnect the electrical connector from the switch.

   Carefully unplug the wiring harness from the faulty switch.

5. 5

   Unclip or unbolt the faulty switch from the seat base.

   Remove the old switch from its mounting position.

6. 6

   Install the new seat switch and secure it in place.

   Note: If your specific seat requires a rocker mechanism for the switch, ensure it is transferred to the new switch or replaced simultaneously.

7. 7

   Reconnect the electrical connector.

   Plug the wiring harness back into the newly installed switch.

8. 8

   Verify the repair.

   Sit in the seat, start the tractor, and activate the VarioGuide steering system to verify the fault code 18.2.05 has cleared and the system engages properly.