Fendt 5.1.9A – Main Tractor ECU / Central Electronics Box (A050): Plausibility error with component S026 (Auxiliary pump flow monitor)

The S026 switch is faulty because it does not close or remains open even when there is no oil flow. The system detects an incorrect voltage or resistance (Ohm) value during its plausibility check when the ignition is ON but the engine is OFF. As a consequence, the system disables pressure monitoring for this circuit.

• 409 Vario
• 410 Vario
• 411 Vario
• 412 Vario
• 711 Vario
• 712 Vario
• 714 Vario
• 715 Vario
• 716 Vario
• 717 Vario
• 718 Vario
• 916 Vario
• 920 Vario
• 924 Vario
• 926 Vario
• 930 Vario
• Fendt 300 Vario Series
• Fendt 400 Vario Series
• Fendt 700 Vario Series
• Fendt 800 Vario Series
• Fendt 900 Vario Series
• 815 Vario
• 817 Vario
• 818 Vario
• Fendt Katana 65 S4

1. 1

   Verify the Fault Timing: The 5.1.9A fault code typically appears 8 seconds after turning the 'Ignition ON'. If cancelled, it will reappear after 10 minutes.

2. 2

   Engine OFF Voltage Check: With the ignition ON and the engine OFF, check the voltage (u) at the S026 switch. The plausibility check requires the voltage to be < 1.1 V.

3. 3

   Engine RUNNING Voltage Check: Start the engine and raise the speed above 1000 RPM. The voltage (u) at the switch must rise to > 1.7 V.

4. 4

   Wiring Inspection: Check the signal line between the S026 connector (Separation point X236) and the central electronics box (e-box) for interruptions, corrosion, or shorts to ground.

1. 1

   Preparation

   Park the tractor on a level surface, turn off the engine, apply the handbrake, and ensure the hydraulic system is completely depressurized.

2. 2

   Locate the Switch

   The S026 switch is located on the right side of the tractor, at the central control valve block. You will need to remove the right-hand side panel/cover to access it.

3. 3

   Disconnect Electricals

   Locate separation point X236, which is the electrical connector for the S026 switch, and unplug it.

4. 4

   Remove the Switch

   Loosen the hydraulic piping connected to the auxiliary pump flow monitor. Carefully unscrew and remove the faulty S026 switch from the valve block.

5. 5

   Install the New Part

   Thread the new switch into the valve block and tighten it to the specified torque. Reconnect the hydraulic piping.

6. 6

   Reconnect and Reassemble

   Plug the X236 electrical connector back into the switch and reinstall the right-hand side cover.

7. 7

   Clear Codes

   Turn the ignition ON, acknowledge/clear the fault code, and run the tractor for at least 10 minutes to ensure the code does not return.