Fendt 1.2.54 – Engine Control Unit (ECU): B086 - Rail pressure sensor: Rail pressure monitoring deactivated

Rail pressure monitoring deactivated. When this fault is triggered, the system will display a warning message indicating that the engine will shut down after approximately 4 to 5 minutes to protect the fuel system.

• 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
• Fendt 400 Vario
• Fendt 700 Vario
• Fendt 800 Vario (e.g., 819, 820 Vario greentec)
• Fendt 900 Vario (e.g., 927, 930, 933, 936, 939)

1. 1

   Check the wiring harness and connectors for the B086 sensor for breaks or short circuits (reference Fendt wiring diagram Sheet 36).

2. 2

   Perform voltage testing at ECU separation point X1671 with Ignition OFF (supply and signal should be 0 VDC).

3. 3

   Perform voltage testing with Ignition ON / Engine Stationary (supply should be 5.0 VDC, signal approx. 0.5 VDC).

4. 4

   Perform voltage testing with Engine Running at no load (Signal should be ~1.37 VDC at 800 rpm, ~2.02 VDC at 1600 rpm, and ~2.24 VDC at 2200 rpm).

5. 5

   Compare the electronic sensor readings against an independent mechanical pressure gauge to rule out a failing high-pressure fuel pump or stuck pressure limiting valve.

1. 1

   Safety Depressurization

   Turn off the diesel engine and wait at least 30 seconds (some heavy-duty guides recommend up to 10 minutes) before starting any work on the fuel system. Disconnect the negative battery terminal.

2. 2

   Clean the Area

   Thoroughly clean the area around the B086 rail pressure sensor on the fuel rail to prevent dirt or debris from contaminating the high-pressure fuel system.

3. 3

   Disconnect Wiring

   Carefully unplug the 3-pin electrical harness connector from the sensor.

4. 4

   Remove the Sensor

   Use the appropriate socket/wrench to unscrew the old sensor from the fuel rail. Have a clean shop towel ready to catch any residual diesel fuel.

5. 5

   Inspect the Port

   Ensure the old sealing washer (if equipped) was removed with the sensor and did not stay stuck in the rail port. Clean the sealing surface.

6. 6

   Install the New Sensor

   If the new sensor utilizes a bite-edge seal, do not use a washer. Lubricate the threads slightly with clean engine oil or specified assembly lube. Thread the new sensor in by hand to prevent cross-threading.

7. 7

   Torque to Spec

   Tighten the sensor using a torque wrench. Always verify the exact torque specification in your specific Deutz/Fendt engine manual to prevent rail damage.

8. 8

   Reassembly & Testing

   Reconnect the electrical connector and the battery. Turn the ignition to the ON position (do not start) and use the SERDIA diagnostic tool to clear fault code FC:00AF. Start the engine and visually inspect the sensor mating surface for any fuel leaks.