Massey Ferguson T139 – TRANS1 (Dyna-6) / TRANS (Dyna-4): High Pressure Brake System Pressure Too Low

Triggers when the pressure in the 50 km/h (31 mph) high-pressure braking unit drops below the minimum threshold (1015 psi / 70 bar) for more than 2 seconds during unit operation.

• 7614
• 7615
• 7616
• 7618
• 7619
• 7620
• 7622
• 7624
• 7626
• Interim Tier 4 (2012-2015)
• MF 7600 Series
• MF 6400 Series
• MF 8600 Series
• 8670

1. 1

   Check System Voltage: Verify the battery voltage and voltage converter.

2. 2

   Inspect the Sensor Connection: Check the high-pressure brake sensor (X495 or B233) to ensure it is not disconnected.

3. 3

   Check for Harness Shorts: Inspect the wiring harness connecting the X495 sensor to the transmission module for shorts to ground or +12V.

4. 4

   Inspect the Accumulator: Check the high-pressure brake accumulator for a faulty or torn accumulator diaphragm.

1. 1

   Locate the Sensor

   Locate the high-pressure brake pressure sensor (X495/B233) on the high-pressure braking unit.

2. 2

   Test the Electrical Circuit

   Disconnect the sensor and use a multimeter to verify that the sensor is receiving the correct reference voltage from the TRANS1 module. Check the ground and signal return wires for continuity.

3. 3

   Replace the Sensor (If Faulty)

   If the wiring is intact but the sensor is reading out of range or failing to register pressure, replace the X495 brake pressure sensor.

4. 4

   Inspect/Replace the Accumulator

   If the sensor and electrical circuits are functioning perfectly, the system is genuinely losing pressure. Depressurize the hydraulic system and remove the high-pressure brake accumulator. Inspect it for internal failure (torn bladder/diaphragm). Replace the accumulator if it cannot hold a charge.

5. 5

   Bleed and Test

   After replacing the sensor or accumulator, bleed the brake system according to the service manual. Clear the fault codes from the TRANS1 module and test drive the tractor at speed to ensure the braking pressure remains above 1015 psi during operation.