Fendt 1.2.D9 – Engine Control Unit (ECU) / A051 (EDC 7): Incorrect voltage for internal 5 V reference source 3

The 3rd 5V reference circuit is outputting an incorrect voltage (either pulled down to ground or shorted to a higher voltage). This circuit specifically supplies power to critical sensors, including the B055 Foot Throttle Sensor and the B086 Rail Pressure Sensor.

• 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
• 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

1. 1

   Disconnect sensors on the 5V reference 3 circuit (B055 foot throttle and B086 rail pressure sensor) one at a time while monitoring the 5V reference line with a multimeter. If voltage returns to normal, the disconnected sensor is internally shorted.

2. 2

   Inspect the wiring harness between the A051 ECU and the sensors for chafed wires, pinched harnesses, or shorts to the chassis (ground) or a 12V power wire.

3. 3

   Locate the A051 Engine Control Unit (behind the battery case at the right entrance step) and inspect connectors X1466 and X1671 for water ingress, corrosion, or bent pins.

4. 4

   Connect FENDIAS / SERDIA diagnostic software to verify the specific sub-fault code FC:00DE.

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the tractor's battery to prevent electrical spikes.

2. 2

   Access the ECU

   Remove the battery case at the right entrance step to access the A051 EDC 7 module.

3. 3

   Repair Wiring/Sensors

   If your diagnostic checks revealed a shorted wire, repair the wiring harness using appropriate weatherproof splices. If a sensor (e.g., B055 or B086) was found to be internally shorted, replace the sensor.

4. 4

   ECU Replacement

   If the wiring is completely intact, all sensors are unplugged, and the ECU still fails to output 5 volts on reference circuit 3, the internal power supply of the EDC 7 module has failed. Remove the ECU and send it to a specialized repair facility for cloning, or install a new unit.

5. 5

   Reassembly

   Reconnect all sensors, ECU connectors, and the battery.

6. 6

   Clear Faults

   Turn the ignition on. You must connect the SERDIA diagnostic software to delete the error (FC:00DE) from the engine control unit. A standard tractor terminal reset will not clear 1.2.xx EDC faults.