Fendt B021 – A050: Rear PTO Speed Sensor Fault

Fault code B021 indicates a signal discrepancy from the rear PTO speed sensing system, specifically the B021 'after clutch' sensor which measures the PTO output stub shaft speed. The system triggers this code when the actual speed read by the sensor differs from the expected speed by more than 12%. This discrepancy points to a faulty sensor, a wiring issue, or a mechanical problem within the PTO system.

• Vario 200 Series
• Vario 300 Series
• Vario 400 Series
• Vario 500 Series
• Vario 700 Series
• Vario 800 Series
• Vario 900 Series
• Farmer 400 Vario Series
• Favorit 511C
• Favorit 512C
• Favorit 514C
• Favorit 515C
• Favorit 700 Series
• Xylon 520
• Xylon 522
• Xylon 524

1. 1

   Retrieve all fault codes using the tractor's onboard diagnostic system (press the 'Enter' key on the console keypad to bring up the error screen, and use the arrow keys to scroll) to confirm if B021 is isolated or part of a larger issue.

2. 2

   Visually inspect the wiring harness leading to the B021 sensor for chafing, corrosion on connectors, or loose pins.

3. 3

   Test the sensor's electrical circuit at the harness side: check for continuity to ground on Pin 1 and verify a stable reference voltage on Pin 2 (Signal) with the key on.

4. 4

   Inspect PTO solenoid valves (Y026, Y027, Y028) for proper operation by checking coil resistance with a multimeter or applying 12V to listen for a click.

5. 5

   Check for mechanical faults in the PTO speed selector mechanism.

1. 1

   Prepare machine

   Park the tractor on a level surface, engage the parking brake, turn off the engine, and block the wheels to prevent movement.

2. 2

   Remove faulty sensor

   Locate the B021 sensor on the rear PTO housing. Disconnect the electrical harness connector, clean the surrounding area to prevent debris from entering the housing, remove the retaining bolt, and carefully pull the old sensor out of its bore (twist it gently to break it free). Do not pull on the cable.

3. 3

   Install new sensor

   Verify the new sensor matches the old one. Lubricate the new O-ring and sensor body with clean hydraulic fluid. Insert the new sensor into the bore, press it firmly into place, and tighten the retaining bolt to the manufacturer's specified torque (do not overtighten).

4. 4

   Verify repair

   Reconnect the electrical connector. Clear the fault codes using the tractor's diagnostic menu, start the tractor, and engage the PTO to verify the repair was successful and the code does not reappear.