Fendt 5.1.51 – A004 Control Console / A002 Enhanced Control ECU: A004 - ECU, control panel; Differential lock 100% button

Key / A004 signal fault. The system is detecting an invalid, missing, or stuck signal from the manual 100% differential lock button located on the control console.

• 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
• 411 Vario COM III
• 412 Vario COM III
• 413 Vario COM III
• 414 Vario COM III
• 415 Vario COM III
• 712 Vario COM III
• 714 Vario COM III
• 716 Vario COM III
• 718 Vario COM III
• 818 Vario COM III
• 820 Vario COM III
• Farmer 400 Vario
• Favorit 700 Vario
• Favorit 900 Vario
• 300 Vario Series
• 400 Vario Series
• 700 Vario Series
• 800 Vario Series
• 900 Vario Series
• 916
• 920
• 924
• 926
• 930

1. 1

   Inspect the 100% differential lock button on the A004 control console to see if the key is mechanically stuck, jammed by debris, or physically broken

2. 2

   Consult the '4WD / Diff. Lock' circuit diagram and test the wiring harness and CAN bus communication lines between the A004 Control Console and the A002 Enhanced Control ECU for continuity or shorts

3. 3

   Check the CAN bus voltage supply on the A013 fuse board, specifically inspecting fuses F040 and F041

1. 1

   Power Down

   Turn off the tractor and disconnect the battery to prevent electrical shorts during testing.

2. 2

   Clean the Switch

   If the differential lock button is sticking, carefully clean the edges of the button on the A004 console with electrical contact cleaner to free it from dirt or spilled liquids.

3. 3

   Test/Repair the Console

   If the switch is a standalone component, test it for electrical continuity. Replace it if it fails to open/close the circuit. Note: If the button is soldered directly into the A004 control console's PCB and has failed internally, the entire A004 console will either need to be replaced or sent to an agricultural electronics specialist for PCB-level repair.

4. 4

   Repair Wiring

   If the switch is functioning but the signal isn't reaching the ECU, repair any broken wires or corroded pins in the harness connecting A004 to A002.

5. 5

   Replace Fuses

   Replace F040 or F041 on the A013 board if they are blown.

6. 6

   Clear Codes

   Reconnect the battery, turn on the ignition, and use the tractor's terminal or the FENDIAS diagnostic tool to clear the 5.1.51 fault code.

7. 7

   Verify Operation

   Test the 100% differential lock engagement to ensure the fault does not return.