Fendt 04.1.89 – Transmission Control System: Plausibility error with the transmission oil temperature

The B009 discharge temperature sensor (or A007 switch) is sending implausible signals to the control unit. The system will log a fault if the sensor readings do not logically match expected operating parameters (e.g., a sudden voltage drop indicating a short circuit, an open circuit, or a faulty sensor) or if the transmission oil temperature exceeds the critical threshold of 110°C.

• 309 Vario COM III
• 310 Vario COM III
• 311 Vario COM III
• 312 Vario COM III
• Fendt 300 Vario (COM III)
• Fendt 400 Vario (COM III)
• Fendt 700 Vario (COM III, SCR)
• Fendt 800 Vario (COM III, S4)
• Fendt 900 Vario (COM III, S4)

1. 1

   Verify Actual Temperature: Determine if the transmission is actually overheating (above 110°C) or if the sensor is simply providing a false reading.

2. 2

   Inspect Wiring and Connectors: Check the wiring harness leading to the B009 sensor (specifically separation point X158) for chafing, breaks, or melted insulation. Inspect the connector for corrosion or loose pins.

3. 3

   Test the Sensor: Use a multimeter to test the resistance of the B009 temperature sensor. Compare the readings against OEM specifications for the current ambient/fluid temperature. An open circuit (infinite resistance) or a dead short indicates a failed sensor.

4. 4

   Check Fluid Levels: Ensure the transmission hydraulic oil (Fendt Extra Trans 10W-40 or STOU oil) is at the correct level and that the suction filters are not clogged, which could cause genuine overheating.

1. 1

   Preparation

   Park the tractor on a level surface, engage the parking brake, turn off the engine, and allow the transmission to cool completely to avoid burns from hot hydraulic oil.

2. 2

   Locate the Sensor

   The B009 discharge temperature sensor is typically located on the right side of the transmission, mounted on the valve block (infeed and discharge area). Note: On many Vario models, accessing this valve block requires removing the right rear wheel and the protective metal panels.

3. 3

   Disconnect Electricals

   Carefully unplug the electrical connector (X158) from the B009 sensor.

4. 4

   Remove the Sensor

   Place a drain pan underneath the valve block to catch any residual transmission oil. Unscrew the faulty B009 temperature sensor from the housing.

5. 5

   Install the New Sensor

   Thread the new OEM temperature sensor (typically an M14x1.5 thread) into the valve block. Tighten to the manufacturer's specified torque to prevent damaging the brass/sensor housing.

6. 6

   Reassembly

   Reconnect the electrical harness. Reinstall the protective metal panels and the right rear wheel (torquing lug nuts to spec).

7. 7

   Fluid Check & Clearing Codes

   Top up the transmission oil if any was lost during the swap. Turn the ignition on and use the tractor's terminal or the FENDIAS diagnostic tool to clear the 04.1.89 fault code. Test drive the tractor to ensure the code does not return.