Fendt A.1.28 – ECU, enhanced control, electric auxiliary control valves (A002 CAN II): Spool valve fault, valve 2 — Main piston cannot return to neutral position because of oil contamination.

Mechanical binding issue within the hydraulic system. The main piston of auxiliary control valve 2 (designated as component Y016) is physically stuck and cannot return to its neutral (center) position due to debris, dirt, or degraded hydraulic oil. This is a DANGER condition, as it can cause undefined and uncontrolled hydraulic functions.

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1. 1

   Inspect the manual actuation slider on Valve 2 (Y016 - typically color-coded blue) to ensure it has no play and snaps back into the middle position by itself.

2. 2

   Pull a sample of the hydraulic oil to inspect for metal shavings, dirt, or severe fluid degradation.

3. 3

   Check the hydraulic filters for heavy contamination or bypass conditions.

4. 4

   Verify valve bus communication to ensure there are no accompanying electrical fault codes (like A.1.20 or A.1.22) that might indicate a CAN bus or voltage drop issue mimicking a stuck valve.

1. 1

   Depressurize the System

   Ensure the tractor is off, implements are lowered, and hydraulic pressure is fully relieved before servicing the valve block.

2. 2

   Drain/Flush Hydraulic Fluid

   If oil contamination is confirmed, drain the contaminated hydraulic oil from the reservoir.

3. 3

   Replace Hydraulic Filters

   Remove and replace the main hydraulic oil filters to prevent re-contaminating the repaired valve.

4. 4

   Remove Valve 2 (Y016)

   Locate auxiliary control valve 2 (blue position) on the hydraulic block. Disconnect the electrical harness (X327 connector) and remove the spool valve.

5. 5

   Clean or Replace the Spool Valve

   Depending on the severity of the scoring on the main piston, the valve must either be thoroughly disassembled, cleaned in a solvent tank, and rebuilt, or replaced entirely if the piston/bore is damaged.

6. 6

   Reinstall and Refill

   Install the cleaned or new spool valve. Refill the system with approved clean hydraulic fluid (e.g., Fendt Super Hyd, Fendt Extra Hyd 68, or STOU SAE 5W-30/40 depending on your specific climate/model requirements).

7. 7

   Clear Codes and Test

   Use the tractor's terminal or the FENDIAS diagnostic tool to clear the A.1.28 fault code. Test the valve manually and electronically to ensure the piston returns to neutral automatically.