Valtra A312 – Autocontrol (AC): Gearbox Oil Temperature Sensor (B14) Impossible Value

The Autocontrol transmission control unit has detected an impossibly low gearbox oil temperature reading (below -50°C) from sensor B14. This implausible value indicates a malfunction within the temperature monitoring circuit, typically caused by a faulty sensor, an open circuit, or a short circuit in the wiring.

• 6000 Series
• 8000 Series
• X100-X120 Series
• A Series
• N Series
• S Series
• T Series

1. 1

   Visually inspect the wiring harness leading to the gearbox oil temperature sensor (B14) on the left-hand side servo valve block for chafing, breaks, or corrosion on the connectors.

2. 2

   Use the tractor's diagnostic test mode (FII) to check the temperature reading from sensor B14 and compare it with the actual ambient temperature of the gearbox oil.

3. 3

   Disconnect the sensor and measure its resistance using a multimeter. Reference values (±1% tolerance): 1600 Ω at 0°C (32°F), 2000 Ω at 25°C (77°F), and 3300 Ω at 100°C (212°F).

4. 4

   Measure the resistance of the sensor circuit from the control unit connector to check for wiring faults (For AC 5 systems, measure at connector X13, between pins 10 and 6).

1. 1

   Ensure Safety

   Park the tractor on a level surface, engage the parking brake, and turn off the engine. Allow the gearbox oil to cool down completely before proceeding to avoid burns.

2. 2

   Drain Gearbox Oil

   Place a suitable container under the gearbox and drain the transmission oil. This will prevent oil spillage when the sensor is removed.

3. 3

   Access the Sensor

   Locate the gearbox oil temperature sensor (B14) on the servo valve block on the left-hand side of the tractor's gearbox.

4. 4

   Disconnect and Remove

   Disconnect the electrical connector from the sensor. Using an appropriate wrench, carefully unscrew and remove the old sensor from the valve block.

5. 5

   Install New Sensor

   Apply a small amount of appropriate thread sealant to the threads of the new sensor. Screw the new sensor into the valve block and tighten it to the manufacturer's specified torque. Do not overtighten.

6. 6

   Reconnect and Refill

   Reconnect the electrical connector to the new sensor. Refill the gearbox with the correct type and amount of transmission oil as specified in the operator's manual.

7. 7

   Final Checks

   Start the tractor and check for any leaks around the new sensor. Clear the fault code from the control unit's memory. Run the tractor and monitor the gearbox oil temperature through the display or diagnostic tool to ensure the new sensor is functioning correctly.