Fendt 1.2.D7 – A051 - ECU, Engine Control Unit (EDC 7): Incorrect voltage for internal 5 V reference source 1

The engine control unit has detected that the 5-volt reference circuit supplying specific engine sensors (B090 and B092) is out of the expected voltage range (either shorted to ground, shorted to voltage, or open).

• 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 (309, 310, 311, 312)
• Fendt 400 Vario COM III (411, 412, 413, 414, 415)
• Fendt 700 Vario COM III (712, 714, 716, 718)
• Fendt 800 Vario COM III (818, 820, 820 greentec)
• Fendt 900 Vario COM III (922, 924, 927, 930, 933, 936)

1. 1

   Identify the Sensors: Locate the B090 Engine Oil Pressure Sensor and the B092 Boost Pressure/Temperature Sensor.

2. 2

   Check the 5V Supply: Using a multimeter, measure the reference voltage at the connectors for B090 and B092 (with the ignition ON, engine OFF). It should read a steady 5 volts.

3. 3

   Isolate the Short: Disconnect B090 and check if the 5V reference returns to normal. If not, reconnect B090 and disconnect B092.

4. 4

   Wiring Harness Inspection: Check the wiring harness and separation points (X1659 for B090, X1661 for B092) for chafing, melted insulation, or corrosion that could cause a short to ground or a short to battery voltage.

5. 5

   Diagnostic Tool: Connect the SERDIA diagnostic software to read out the KWP code, monitor live sensor voltages, and confirm the fault.

1. 1

   Power Down

   Turn off the tractor ignition and wait at least 30 seconds for the EDC 7 ECU to power down completely before disconnecting any engine sensors.

2. 2

   Repair Wiring (If Applicable)

   If the diagnostic checks revealed a short circuit or broken wire in the harness between the A051 ECU and the B090/B092 sensors, repair the damaged wiring or replace the affected harness section.

3. 3

   Replace Faulty Sensor (If Applicable)

   If disconnecting one of the sensors restored the 5V reference circuit, that sensor has an internal short. To replace B090: Clean the area around the oil filter base, unscrew the old oil pressure sensor, install the new sensor, and reconnect the harness. To replace B092: Remove the boost pressure/temperature sensor from the intake manifold/charge pipe, install the new combi-sensor, and reconnect the harness.

4. 4

   ECU Repair (Worst-Case Scenario)

   If the wiring is perfectly intact and the sensors are not shorted, but the A051 ECU is still failing to output 5 volts on Reference Source 1, the Bosch EDC7UC31 module itself has suffered an internal hardware failure. The ECU will need to be removed and sent to a specialized agricultural electronics repair facility or replaced.

5. 5

   Clear Faults

   Reconnect all components. Turn the ignition on and use the SERDIA diagnostic tool to delete the error (FC:00DB) from the A051 memory.