Fendt 5.1.9A – Central ECU (A050 - ECU, basic control unit) / E-box: Plausibility check error on the steering pump flow controller (Component S026)

The system detects that the switch is faulty because it does not close or remains open even when there is no oil flow. It registers an incorrect voltage or Ohm value during the plausibility check.

• 411 Vario COM III
• 412 Vario COM III
• 413 Vario COM III
• 414 Vario COM III
• 415 Vario COM III
• 712 Vario COM III
• 714 Vario COM III
• 716 Vario COM III
• 718 Vario COM III
• 818 Vario COM III
• 820 Vario COM III
• Fendt 300 Vario (COM III)
• Fendt 400 Vario (e.g., 409, 410, 411, 412)
• Fendt 500 Vario (S4 Series)
• Fendt 700 Vario (e.g., 711, 712, 714, 716)
• Fendt 800 Vario (e.g., 815, 817, 818)
• Fendt 900 Vario / Favorit 900 (e.g., 916, 920, 924, 926, 930, 936)

1. 1

   Engine OFF Test: Turn the ignition ON with the engine OFF. Measure the voltage at the S026 switch. The voltage must be < 1.1 V.

2. 2

   Engine RUNNING Test: Start the engine and raise the speed above 1000 RPM. The voltage must rise to > 1.7 V.

3. 3

   Wiring Inspection: Check the signal line between the E-box and the S026 connector (Separation point X236) for interruptions, short circuits to earth, or corrosion.

4. 4

   Switch Continuity: Test the switch itself to see if it is physically stuck open. If the switch fails to close without oil flow, the switch has failed internally.

1. 1

   Preparation

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

2. 2

   Locate the Component

   The S026 steering pump flow controller switch is located on the right side of the tractor, at the central valve block / control valves.

3. 3

   Access the Valve Block

   Detach and remove the protective side panel/cover on the right side to expose the central valve block.

4. 4

   Disconnect Wiring

   Locate the S026 switch and disconnect its electrical connector (designated as separation point X236).

5. 5

   Remove the Switch

   Unscrew the faulty S026 switch from the hydraulic valve block. Have a rag ready to catch any residual hydraulic oil that may weep from the port.

6. 6

   Install the New Part

   Thread the new flow controller switch into the valve block and tighten it to the manufacturer's specified torque.

7. 7

   Reconnect

   Plug the X236 electrical connector back into the new switch.

8. 8

   Reassembly & Clearing Codes

   Reinstall the right-side protective panel. Turn the ignition ON, clear the fault code via the tractor's terminal or diagnostic tool, and run the tractor above 1000 RPM to verify the code does not return after 10 minutes.