Deutz-Fahr T79 – Transmission Control Unit (TCU): FORWARD drive SV disconnected

The electronic control unit has detected an open circuit or that the forward drive selector solenoid valve (Y3 or Y6) is physically disconnected or has a broken internal coil.

• Agroplus 310, 320, 410, and 420 Profiline series tractors
• Deutz-Fahr Agrofarm (410, 420, 430)
• Deutz-Fahr Agroplus (60, 70, 80)
• Deutz-Fahr Agrotron (MK3, K, M, and X series)
• Deutz-Fahr R3 Evo (85, 100, 110)
• Deutz-Fahr R8 (230, 270 DCR)
• SAME Explorer 90

1. 1

   Inspect the wiring harness between the TCU and the transmission valve block, specifically checking contacts on connector X54 of the shuttle ECU and connector X60 of the forward drive solenoid valve for looseness or corrosion.

2. 2

   Verify that the forward drive solenoid valve is receiving the correct 12V power supply when forward drive is commanded.

3. 3

   Test the internal resistance of the forward drive solenoid coil using a multimeter to confirm if the coil has failed (open circuit).

1. 1

   Locate the Valve Block

   The hydraulic gearbox and shuttle distribution valve block is typically located on the right-hand side of the tractor, under the driving platform.

2. 2

   Drain the Oil

   Place a large container (at least 33 liters capacity) under the rear gearbox and unscrew the oil drain plug to drain the transmission fluid.

3. 3

   Remove the Faulty Valve

   Disconnect the electrical connector from the Forward drive pilot solenoid valve (Y3 or Y6). Unbolt and remove the solenoid valve assembly along with its relative seals.

4. 4

   Install the New Valve

   Fit the new solenoid valve with fresh O-rings/seals into the distribution block.

5. 5

   Reassemble and Refill

   Reconnect the wiring harness. Reinstall the drain plug and refill the transmission with the manufacturer-specified hydraulic/transmission oil.

6. 6

   Perform Calibration

   Move the shuttle lever to neutral, then move it back to the travel direction. Wait until the display reads “CALIB. TERMINATED”, then press “E” to save the new calibration values.