Fendt 5.1.99 – A050 - ECU (Basic Control Unit): S026 - Switch, steering pump flow controller failure

Minimum hydraulic flow cannot be reached or the signal from the flow control sensor is disturbed. At engine speeds greater than 1000 rpm, the voltage signal from the S026 switch must be > 1.7 V. If the flow monitor does not open or the minimum pressure/flow is not detected, the fault is triggered.

• 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
• Farmer 400 Vario
• Favorit 700 Vario
• Favorit 900 Vario
• 500 Vario series
• 800 Vario series
• 1000 Vario series

1. 1

   Perform a plausibility check with the engine OFF: verify the voltage of the steering pump flow monitor is < 1.1 V.

2. 2

   Perform an operational check with the engine ON: run the engine at > 1000 rpm. The voltage should rise above 1.7 V. If it reads 0 V, the flow monitor is not opening.

3. 3

   Inspect the wiring and signal line for a short-circuit to earth (test sequence: 0/0 V). Check the X236 separation point (S026 switch connector) for corrosion or damage.

4. 4

   Verify the actual oil pressure on the auxiliary pump (constant displacement pump) to rule out a genuine mechanical failure of the pump.

1. 1

   Locate the Switch

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

2. 2

   Preparation

   Turn off the engine, apply the handbrake, and ensure the hydraulic system is depressurized. Remove the right-side cover panel to access the central valve block.

3. 3

   Disconnect

   Unplug the electrical connector (X236) from the S026 switch.

4. 4

   Removal

   Unscrew the faulty flow controller switch from the valve block. Have a rag ready to catch any residual hydraulic oil.

5. 5

   Installation

   Thread the new S026 switch into the valve block and tighten to the manufacturer's specified torque.

6. 6

   Reconnect

   Plug the X236 electrical connector back into the switch.

7. 7

   Test and Clear

   Reinstall the cover panel. Start the tractor and run the engine above 1000 rpm. Perform a key reset/restart to clear the active 5.1.99 fault code and verify that the control valve flow is restored to normal capacity.