Fendt A.1.29 – ECU, enhanced control, electric auxiliary control valves (A002): Spool valve fault, valve 2 — Main piston cannot return to neutral position when switched on because of oil contamination.

This code indicates that the main piston inside auxiliary control valve 2 (Y016, typically color-coded blue) is physically sticking or binding. Because of debris or contaminated hydraulic fluid, the piston is unable to center itself back to the neutral position when commanded.

• 409 Vario
• 410 Vario
• 411 Vario
• 412 Vario
• 711 Vario
• 712 Vario
• 714 Vario
• 715 Vario
• 716 Vario
• 717 Vario
• 718 Vario
• 916 Vario
• 920 Vario
• 924 Vario
• 926 Vario
• 930 Vario
• Farmer 400 Vario series
• Favorit 700 and 700 Vario series (COM I, II, III)
• Favorit 800 and 800 Vario series
• Favorit 900 and 900 Vario series (COM I, II, III)

1. 1

   Check the hydraulic oil for visible signs of contamination (metal shavings, dirt, water intrusion, or degraded oil).

2. 2

   Verify that the hydraulic control pressure is not dropping below 22 bar, which can exacerbate valve return issues.

3. 3

   Check the manual actuation slider on Valve 2. It must not have excessive play and must spring back into the middle position smoothly.

4. 4

   Ensure there are no accompanying fault codes for the internal position sensor (e.g., A.1.27) or supply voltage issues (e.g., A.1.23) that might mimic a mechanical bind.

1. 1

   Relieve Pressure

   Safely lower all hydraulic implements to the ground, turn off the engine, and relieve all hydraulic pressure from the system.

2. 2

   Isolate Valve 2 (Y016)

   Locate the auxiliary control valve block. Valve 2 is typically the second slice (often marked with a blue decal or cap).

3. 3

   Remove and Inspect

   Disconnect the electrical connector (X327) and hydraulic lines to Valve 2. Remove the valve slice from the stack.

4. 4

   Clean and Flush

   Because the root cause is oil contamination, the valve must be disassembled and thoroughly cleaned. Inspect the main piston and the valve bore for scoring.

5. 5

   System Flush

   If heavy contamination is found, you must drain the hydraulic oil, replace the hydraulic filters, and flush the system to prevent the debris from immediately destroying the repaired or replaced valve.

6. 6

   Replace or Rebuild

   If the piston or bore is scored, the valve slice cannot be saved and must be replaced.

7. 7

   Reassembly and Calibration

   Install the new or cleaned valve slice. Reconnect the X327 connector.

8. 8

   Clear Codes and EOL Programming

   Use the FENDIAS diagnostic tool to clear the A.1.29 fault code. If a brand-new valve is installed, it must be registered and calibrated to position 2 via the EOL (End of Line) programming software.