Fendt 04.1.78 – Transmission Control Unit / Basic Control Unit (ECU A050), Enhanced Control ECU (A002), or Multifunction Armrest (MFA - A039 / A100): S053 - Switch, driver seat (Driver presence switch)

The system detects a 'Signal fault' or a 'Faulty switch.' This typically means the seat is not registering as 'loaded' (operator sitting in it) when steering or travel is activated, or there is an open/short circuit in the switch wiring. Consequently, the TMS is automatically switched off and travel direction selection is deactivated in accelerator pedal mode when the vehicle is stationary.

• 309 Vario COM III
• 310 Vario COM III
• 311 Vario COM III
• 312 Vario COM III
• 922 Vario COM III
• 924 Vario COM III
• 927 Vario COM III
• 930 Vario COM III
• 933 Vario COM III
• 936 Vario COM III
• Fendt 300 Vario (COM III)
• Fendt 400 Vario (COM III)
• Fendt 700 Vario (COM III / SCR)
• Fendt 800 Vario (COM III / S4)
• Fendt 900 Vario (COM III / S4)

1. 1

   Verify that the seat is actually loaded (an operator is sitting in it with enough weight to trigger the switch).

2. 2

   Inspect the electrical connector (X830) and wiring harness under the seat for loose connections, corrosion, or pinched wires.

3. 3

   Test the S053 switch resistance and voltage with a multimeter. Seat NOT loaded (switch open) should be approximately 510 ohms (~6.1 VDC). Seat LOADED (switch closed) should be approximately 121 ohms (~1.8 VDC).

1. 1

   Power down tractor

   Power down the tractor and disconnect the battery or the power supply to the seat to prevent short circuits.

2. 2

   Locate switch

   Locate the S053 seat switch, which is integrated under the driver's seat cushion (standard Grammer air-suspension seats).

3. 3

   Disconnect connector

   Disconnect the electrical connector (X830) leading to the switch.

4. 4

   Remove switch

   Remove the faulty seat switch assembly.

5. 5

   Transfer rocker mechanism

   If you are installing a bare replacement switch (e.g., Grammer 1141805), you must carefully remove the plastic rocker mechanism (part 1100731) from the old switch and transfer it to the new one.

6. 6

   Install new switch

   Install the new switch assembly into the seat cushion frame and reconnect the electrical harness.

7. 7

   Clear codes and test

   Power on the tractor, clear the stored fault codes via the FENDIAS diagnostic program or the tractor's dashboard menu, and test the seat presence detection by sitting in the seat and verifying that TMS and travel direction selection function normally.