Fendt 4.1.33 – Transmission Control Unit (Twin EST Modules): Automatic maximum output control' key on membrane keypad — Signal fault

The electronic control unit is receiving an invalid signal from the 'Automatic maximum output control' button on the armrest's membrane keypad. This is typically due to a hardware failure within the membrane switch itself (such as a stuck, collapsed, or short-circuited button) or an open circuit in the wiring, which causes the automatic maximum output control function to be disabled.

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1. 1

   Inspect the membrane keypad on the multifunction armrest for physical damage, tearing, or a collapsed 'Load limit control' button that might be permanently stuck down.

2. 2

   Use the FENDIAS diagnostic tool or the tractor's onboard diagnostic terminal to monitor the live input status of the keypad, checking if the button's signal is registering as permanently active (shorted) or completely dead (open circuit).

3. 3

   Check the wiring harness and ribbon connectors between the armrest comfort module and the Twin EST transmission control modules for pinched wires, corrosion in the connector pins, or loose connections.

1. 1

   Disconnect Power

   Disconnect the tractor's battery to prevent electrical damage or short circuits during disassembly.

2. 2

   Disassemble the Armrest

   Remove the retaining screws on the multifunction armrest console to access the internal comfort module and the underside of the membrane keypad.

3. 3

   Disconnect the Keypad

   Carefully unlatch and disconnect the delicate ribbon cable or wiring harness connecting the membrane keypad to the main comfort module board.

4. 4

   Test / Replace the Component

   If the wiring harness is intact and the fault is isolated to the keypad, replace the keypad or the entire armrest comfort module. If using an aftermarket repair kit, peel off the old membrane sticker, clean the adhesive residue thoroughly, apply the new membrane keypad, and seat the new ribbon cable.

5. 5

   Reassembly

   Reconnect the ribbon cable to the board and reassemble the armrest console housings.

6. 6

   Clear Codes

   Reconnect the battery, turn on the ignition, and use the terminal or FENDIAS to clear the stored 4.1.33 fault code. Test the 'Automatic maximum output control' button to ensure the function engages properly.