Fendt 1.2.1A – Engine Control Unit (EDC) / A021: B026 - Needle movement sensor NBF (EDC) — Signal fault

The Engine Control Unit is receiving an incorrect, missing, or out-of-range signal from the B026 Needle Movement Sensor (NBF). This causes the engine control to switch to a restricted operating mode, resulting in reduced engine speed, reduced engine power, and altered engine control parameters.

• 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
• 309 Vario
• 310 Vario
• 311 Vario
• 312 Vario
• 815 Vario
• 817 Vario
• 818 Vario

1. 1

   Inspect the electrical connector at the B026 sensor (on the injector) and trace the wiring harness back to the EDC control module (A021) for chafed wires, melted insulation, or corrosion.

2. 2

   Measure the resistance of the needle movement sensor coil using a multimeter to verify if the internal coil has failed (open circuit or short).

3. 3

   Use FENDIAS or SERDIA diagnostic software to monitor the 'Start of Injection' and the live signal from the B026 sensor. If the signal drops out intermittently when the wiring is wiggled, the harness is the culprit. If the signal is completely dead but wiring tests good, the sensor/injector has failed.

1. 1

   Turn off the tractor, remove the key, and disconnect the battery.

   Ensure the machine is fully powered down before beginning the repair.

2. 2

   Clean the area around the affected injector.

   Clean around the injector with the electrical wire protruding from it to prevent dirt from entering the engine block.

3. 3

   Disconnect the electrical connector for the B026 sensor.

   Carefully unplug the sensor connector.

4. 4

   Loosen and remove the high-pressure fuel line.

   Disconnect the line connecting the injection pump to the injector and cap the open fittings.

5. 5

   Remove the injector hold-down clamp or retaining bolt.

   Unbolt the hardware securing the injector in place.

6. 6

   Carefully pull the injector out of the cylinder head.

   Extract the injector assembly from the engine block.

7. 7

   Thoroughly clean the injector bore.

   Crucial: Ensure the old copper sealing washer is removed from the bore and not stuck at the bottom.

8. 8

   Prepare the new injector with a new copper sealing gasket.

   Lightly grease a new copper sealing gasket and place it onto the nozzle of the new injector (the grease holds it in place during installation).

9. 9

   Insert the new injector into the bore.

   Note: Fendt/MAN service manuals recommend using a special slotted socket tool (MAN 80996030246) to lead the sensor cable through so you can torque the injector without crushing the delicate sensor wire.

10. 10

    Reinstall the hold-down clamp/bolt.

    Torque the retaining hardware to OEM specifications.

11. 11

    Reconnect the high-pressure fuel line and the electrical connector.

    Ensure all fuel and electrical connections are secure.

12. 12

    Finalize the repair and clear the fault code.

    Reconnect the battery, bleed the fuel system if necessary, start the engine, and use your diagnostic tool to clear the 1.2.1A fault code.