Massey Ferguson T151 – TRANS1 / Autotronic 5: High Pressure Brake System Pressure Dropped To Quickly

This condition occurs when the system detects an abnormally fast loss of hydraulic pressure in the braking circuit. The most common underlying causes are a failed or discharged high-pressure brake accumulator, a hydraulic leak, or a faulty brake pressure sensor.

• 7614
• 7615
• 7616
• 7618
• 7619
• 7620
• 7622
• 7624
• 7626
• Interim Tier 4 (2012-2015)
• 5400 Series
• 6400 Series
• 6445
• 6455
• 6460
• 6485
• 6600 Series
• 6612
• 6613
• 6614
• 6615
• 6616
• 7600 Series
• 7700 Series

1. 1

   Perform an accumulator pre-charge test with the engine stopped to check the nitrogen gas pressure in the high-pressure braking unit accumulator (Accumulator 'Q'). Pressure must be between 53 to 56 bar

2. 2

   Inspect the 50 km/h brake pressure sensor (X495) and its wiring harness for open circuits, shorts to 12V/0V, or physical damage to the connector

3. 3

   Visually inspect the high-pressure braking block, brake master cylinder, and all hydraulic lines for external leaks

4. 4

   Check transmission/hydraulic oil level and ensure the high-pressure transmission oil filter is not blocked

1. 1

   Depressurize the System

   Turn off the tractor engine. Pump the brake pedals multiple times to safely discharge any residual hydraulic pressure in the accumulators and brake lines.

2. 2

   Replace/Recharge the Accumulator

   If the accumulator (HYDAC SBO210) failed the pressure test (below 53 bar) or has a ruptured internal diaphragm, unscrew it from the high-pressure braking block and install a new unit. If the diaphragm is intact but pressure is low, it can be recharged with nitrogen by a qualified hydraulic technician.

3. 3

   Replace the Brake Pressure Sensor

   If diagnostics point to sensor X495, disconnect the electrical harness, unthread the sensor from the braking unit, install the replacement sensor, and reconnect the harness.

4. 4

   Repair Leaks

   If a leak was found at the master cylinder or hydraulic lines, replace the damaged hoses or install a master cylinder repair kit.

5. 5

   Bleed the Brakes

   If the hydraulic circuit was opened during the repair, bleed the brake system according to the service manual to remove trapped air.

6. 6

   Clear Codes and Test

   Use a diagnostic tool to clear the T151 fault code from the Autotronic 5 / TRANS1 module. Start the tractor, allow the brake system to charge, and test drive to ensure braking pressure holds steady without dropping too quickly.