Fendt 0F.1.1B – A038 - ECU, central electrical system: Processor supply voltage too high or too low

The internal voltage regulator within the Central Electrical System ECU is detecting a voltage level outside of its normal operating parameters. This can be caused by a general tractor overvoltage/undervoltage condition, a wiring issue, or an internal hardware failure within the ECU itself.

• 922 Vario COM III
• 924 Vario COM III
• 927 Vario COM III
• 930 Vario COM III
• 933 Vario COM III
• 936 Vario COM III
• FENDT 300 Vario (COM III)
• FENDT 400 Vario (COM III)
• FENDT 700 Vario (COM III)
• FENDT 800 Vario (COM III)
• FENDT 900 Vario (COM III) (Models 919, 922, 925, 928, 931, 934, 936)

1. 1

   Test the tractor's battery voltage and alternator output to ensure the main system voltage is within the normal 12V–14V range.

2. 2

   Inspect the wiring harness and connectors (e.g., X454, X455) at the A038 ECU for corrosion, moisture ingress, or loose pins.

3. 3

   Check the power supply relays (e.g., Relay 15E, Relay 15L) and the microfuses on PCB A013 that feed the central electrical system.

4. 4

   Test the total resistance of the K-bus. It should normally be 60 Ohms (Note: On older 900 Vario tractors up to chassis 9XX/2X/1701, an additional 120-ohm terminating resistor was installed in the A038 ECU, making the total resistance 40 Ohms).

5. 5

   Check the voltage level of CAN High/CAN Low (0 VDC = earth connection, 4 VDC and higher = short circuit to +UB).

6. 6

   Use a 160-pin adapter box to test the pin-out supply voltages directly at the A038 ECU to verify it is receiving the correct external voltage.

1. 1

   Disconnect Power

   Disconnect the tractor's battery before performing any electrical repairs or unplugging modules.

2. 2

   Verify External Power

   If the adapter box test confirms that the A038 ECU is receiving the correct external supply voltage and ground, but the 0F.1.1B code remains active, the ECU has suffered an internal processor voltage failure.

3. 3

   Remove the ECU

   Locate the A038 Central Electrical System ECU (typically located in the cab/dashboard area or behind the right mudguard panel, depending on the specific Vario model) and carefully disconnect the wiring harnesses.

4. 4

   Repair or Replace

   Because this is an internal hardware failure, the A038 ECU must either be sent to a specialized agricultural electronics repair service (such as EPS-Elektronik) for internal board repair, or replaced entirely.

5. 5

   Reinstallation

   Install the repaired or replacement A038 ECU and reconnect the wiring harnesses.

6. 6

   EOL Programming

   If a new or replacement ECU is installed, you must perform End-of-Line (EOL) programming and calibration using FENDIAS diagnostic software. Without EOL programming, the ECU will not communicate properly with the K-bus network.

7. 7

   Final Testing

   Clear the fault codes using FENDIAS and test the tractor's electrical functions (lights, wipers, A/C) to verify the repair.