Fendt 4.1.86 – Transmission Control Unit (A050 basic control unit ECU): B008, B039 - High pressure sensor I / High pressure sensor II — Plausibility error

This code indicates a plausibility error between the readings of sensor B008 (High-pressure sensor I, monitoring transmission drive pressure) and sensor B039 (High-pressure sensor II, monitoring push detection). The transmission control unit constantly compares the values from both sensors; if the pressure readings do not logically match each other under current operating conditions, the system flags the data as implausible. This causes the tractor to lose enhanced control functions during drive operation, disables the Active parking function, switches off the TMS, and restricts transmission automation.

• 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
• 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
• 309 Vario
• 310 Vario
• 311 Vario
• 312 Vario COM III / SCR / S4
• 815 Vario
• 817 Vario
• 818 Vario
• 820 Vario
• 927 Vario
• 933 Vario
• 936 Vario
• 939 Vario

1. 1

   Use the Variotronic Ti terminal (A008) to view live data on the transmission diagnostics page. Monitor live oil pressure readings from B008 and B039 for erratic jumping, sticking at 0 bar, or maxing out.

2. 2

   Test the signal voltage and current draw of the sensors with a multimeter (engine speed above 1400 rpm). Expected values: ~0.80 VDC / 4.0 mADC at 0 bar, ~0.94 VDC / 4.7 mADC at 30 bar, ~1.37 VDC / 6.7 mADC at 100 bar, and ~3.80 VDC / 18.7 mADC at 560 bar.

3. 3

   Verify that the sensors are receiving their required 8.5 VDC supply voltage (supplied via A013 fuse). Inspect the wiring harness and separation points (Connector X157 for B008, Connector X177 for B039) for corrosion, moisture, or wire breaks.

4. 4

   If electrical readings are erratic, verify the actual transmission pressure using a manual hydraulic pressure gauge on the test ports to rule out internal hydrostatic pump/motor issues.

1. 1

   Access the Sensors

   Safely support the tractor, remove the right rear wheel, and take off the protective metal side panels to access the B008 and B039 sensors located on the right side of the transmission, mounted directly on the hydraulic valve block.

2. 2

   Removal

   Clean the area thoroughly around the faulty sensor to prevent dirt ingress into the hydrostatic circuit. Disconnect the electrical connector (X157 or X177) and unscrew the sensor from the hydraulic manifold port.

3. 3

   Installation

   Ensure the new O-ring is lubricated with clean transmission oil and installed on the new sensor. Thread the new sensor into the port and tighten to OEM torque specifications.

4. 4

   Reassembly

   Reconnect the electrical harness. Reinstall the protective metal panels and the right rear wheel.

5. 5

   Calibration

   Clear the fault codes using the diagnostic terminal. Run the EOL (End of Line) transmission calibration if required by the service manual. Note: A functional B008 high-pressure sensor must be installed in order to successfully run the transmission calibration procedure.