Fendt 04.1.73 – Transmission Control Unit (TCU): Signal fault from the B009 'Discharge oil temperature' sensor

The control unit has detected an electrical anomaly (such as an open circuit, a short circuit, or an implausible reading) from the B009 'Discharge oil temperature' sensor. The system provides no further display or monitoring of the transmission temperature, which can lead to severe transmission damage if the tractor is operated while actually overheating.

• 309 Vario COM III
• 310 Vario COM III
• 311 Vario COM III
• 312 Vario COM III
• Fendt 300 Vario
• Fendt 400 Vario / Farmer 400
• Fendt 700 Vario / Favorit 700
• Fendt 800 Vario
• Fendt 900 Vario / Favorit 900

1. 1

   Inspect the wiring harness and the electrical connector leading to the B009 sensor on the transmission housing for broken wires, chafing, or corroded pins.

2. 2

   Use the tractor's terminal or a diagnostic tool (FENDIAS / SERDIA) to read the live transmission oil temperature. Impossible values (e.g., constantly showing < 50°C or instantly spiking to > 120°C on a cold machine) confirm a faulty sensor or wiring.

3. 3

   Disconnect the sensor and test its internal resistance with a multimeter. Compare the reading against OEM specifications for the ambient temperature to determine if the sensor has an internal open or short circuit.

1. 1

   Preparation

   Park the tractor on a level surface, engage the parking brake, and turn off the engine. Allow the transmission to cool if it has been running.

2. 2

   Locate the Sensor

   Locate the B009 Discharge oil temperature sensor. It is threaded into the Vario transmission housing, typically near the transmission oil filter and high-pressure circuit lines.

3. 3

   Clean the Area

   Thoroughly clean the area around the sensor to prevent dirt or debris from entering the transmission hydraulic circuit when the sensor is removed.

4. 4

   Removal

   Disconnect the electrical connector. Unscrew the faulty B009 sensor using a wrench. Have a catch pan ready, as a small amount of transmission fluid will leak out.

5. 5

   Installation

   Thread the new temperature sensor into the port and tighten it to the manufacturer's specified torque.

6. 6

   Reconnection

   Reconnect the electrical wiring harness, ensuring the connector clicks securely into place.

7. 7

   Fluid Check

   Check the transmission oil level and top up with the correct specification fluid (e.g., Fendt Extra Trans 10W-40 or STOU) if a significant amount was lost.

8. 8

   Clear Codes

   Turn on the ignition and use the tractor's terminal or FENDIAS diagnostic software to clear the stored 04.1.73 fault code. Test drive the tractor to ensure the code does not return.