Fendt 05.1.9C – A050 - ECU, basic control unit: Plausibility error with S075 - Switch, guard rail pump flow monitor

A plausibility error with the S075 switch (guard rail pump flow monitor). When the tractor is stationary and during reverse travel, the signal voltage (u) from this switch must be less than 1.1 V. If the voltage exceeds this threshold under these conditions, the system logs the 05.1.9C fault.

• 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
• Fendt 400 Vario (e.g., 409, 411, 412, 413, 414, 415)
• Fendt 500 Vario (e.g., 512, 513)
• Fendt 700 Vario
• Fendt 800 Vario
• Fendt 900 Vario (e.g., 922, 924, 927, 930, 933, 936, 939)

1. 1

   Monitor the S075 switch voltage via the tractor's diagnostic terminal to verify if voltage is < 1.1 V when stationary and in reverse.

2. 2

   Test the wiring harness at the S075 switch to ensure the A050 Basic Control ECU is supplying the correct 6.0 VDC basic signal voltage.

3. 3

   Inspect the wiring harness for shorts to power or ground (refer to Circuit diagram Sheet 7 for the guard rail pump flow monitor circuit).

1. 1

   Locate the Sensor

   The S075 switch is located on the hydraulic central valve block. On models like the 500/700 Vario, the separation point (X1499) for S075 is found on the right side of the tractor at the central valve block. You will need to detach the protective cover to access it.

2. 2

   Prepare for Fluid Loss

   Because this is a hydraulic flow sensor integrated with a high-pressure filter, place a catch pan beneath the valve block to catch escaping hydraulic fluid.

3. 3

   Disconnect Electronics

   Unplug the electrical connector from the S075 sensor.

4. 4

   Remove the Assembly

   Unscrew and remove the faulty flow sensor and filter assembly.

5. 5

   Install the New Part

   Install the replacement sensor/filter unit. Ensure any O-rings or seals are properly seated to prevent high-pressure leaks.

6. 6

   Reconnect and Clear

   Reconnect the electrical harness. Turn on the tractor, navigate to the fault code memory, and clear the active/stored 05.1.9C code.

7. 7

   Verify Repair

   Keep the tractor stationary and shift into reverse to confirm the fault does not return and the sensor voltage remains below 1.1 V.