Fendt 0F.1.19 – A038 - Central electrical system ECU: A038 - ECU, central electrical system: Sensor supply voltage too high or too low

The central electrical system ECU detects an improper voltage level on its sensor supply circuit. As a safety and operational consequence, multiple cab and chassis functions are disabled, including the windshield wipers, water valve, primary fan, work lights, hydraulic relay circuits 3 and 4, rear window heater, reverse operation, and the tank pump.

• 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 820 Vario greentec
• Fendt 900 Vario (COM III)
• Fendt 922 Vario (COM III)
• Fendt 924 Vario (COM III)
• Fendt 927 Vario (COM III)
• Fendt 930 Vario (COM III)
• Fendt 933 Vario (COM III)
• Fendt 936 Vario (COM III)

1. 1

   Measure the sensor supply voltage entering the A038 ECU to determine if there is a short to ground (voltage too low) or a short to battery voltage (voltage too high).

2. 2

   Inspect the central electrical system microfuses (PCB A013) and relays associated with disabled functions (e.g., K7 primary fan, K18 rear window heater, K6/K8 hydraulic circuits) for shorts.

3. 3

   Test the K-Bus total resistance of the passive bus. It should be 60 Ohms (or 40 Ohms on older 900 Vario tractors up to chassis 9XX/2X/1701).

4. 4

   Check the voltage level of CAN High/CAN Low. 0 VDC indicates a short to ground, while 4 VDC or higher indicates a short circuit to battery positive.

5. 5

   Use the Fendt OEM adapter box to isolate and test the A038 ECU directly to rule out external wiring harness shorts.

1. 1

   Isolate the Short

   Disconnect the sensors and actuators on the affected circuit (wipers, fans, work lights, etc.) one by one while monitoring the sensor supply voltage at the A038 ECU. If the voltage returns to normal, the last disconnected component (or its wiring) is shorted.

2. 2

   Inspect the Wiring Harness

   Check the wiring harness routing from the A038 ECU (typically located in the cab/dashboard area) to the affected relays and sensors for chafing, pinched wires, or melted insulation. Repair any damaged wiring.

3. 3

   Test/Replace the ECU

   If the wiring harness and all external components test good, but the A038 ECU still outputs an incorrect sensor supply voltage, the internal power supply of the ECU has failed and the ECU must be replaced.

4. 4

   EOL Programming

   If the A038 ECU is replaced, the new module will require EOL (End of Line) programming via FENDIAS (Fendt Diagnostic System) to communicate properly with the tractor's K-bus.