Fendt 01.2.C0 – A039 - MFA (Multifunction Armrest): Warning message "Seat switch with active TMS"

This fault indicates a safety interlock conflict. The Tractor Management System (TMS) is currently active, but the driver presence switch (S053) in the seat is reporting that the operator's seat is unoccupied. As a safety consequence, the TMS automatically switches off.

• 922 Vario COM III
• 924 Vario COM III
• 927 Vario COM III
• 930 Vario COM III
• 933 Vario COM III
• 936 Vario COM III
• 309
• 310
• 311
• 312
• 409
• 410
• 411
• 412
• 711
• 712
• 714
• 715
• 716
• 717
• 815
• 817
• 818
• 916
• 920
• 924
• 926
• 930
• 936

1. 1

   Ensure the operator is sitting fully and squarely in the seat when the TMS is engaged. Light operators or sitting on the edge of the seat can cause the switch to disengage.

2. 2

   Locate the S053 driver presence switch connector under the seat and use a multimeter to test for continuity when weight is applied to and removed from the seat cushion.

3. 3

   Inspect the wiring harness and connectors between the S053 seat switch and the A039 MFA module for chafing, pin corrosion, or broken wires.

4. 4

   Ensure the mechanical or pneumatic suspension of the Grammer seat is not jammed, preventing the seat cushion from properly actuating the switch rocker.

1. 1

   Prepare tractor for service

   Park the tractor on a level surface, engage the parking brake, and turn off the ignition.

2. 2

   Disconnect battery

   Disconnect the tractor's battery to prevent electrical shorts during repair.

3. 3

   Remove seat cushion

   Remove the seat cushion from the seat base (Fendt tractors typically use Grammer MSG 83/85/93/95 series seats).

4. 4

   Locate switch

   Locate the S053 driver presence switch and its actuating rocker mechanism inside the seat base.

5. 5

   Disconnect electrical connector

   Disconnect the electrical connector from the switch.

6. 6

   Remove faulty switch

   Unhook the retaining spring and remove the rocker to free the faulty switch.

7. 7

   Install new switch

   Install the new seat switch and reattach the rocker and spring mechanism.

8. 8

   Reassemble seat

   Reconnect the electrical harness and reinstall the seat cushion.

9. 9

   Clear fault codes

   Reconnect the battery, turn on the ignition, and clear the stored fault codes using the Varioterminal or FENDIAS diagnostic software.

10. 10

    Test repair

    Test the repair by sitting in the seat, engaging the TMS, and verifying that the system remains active and the warning message does not reappear.