Fendt 0F.1.1A – A038 - ECU, central electrical system: Main supply voltage too high (>18V for 5 minutes)

The fault code 0F.1.1A indicates a critical power supply issue: Main supply voltage too high (>18V for 5 minutes). Some older or generalized manuals also list this code as 'Main supply voltage too high or too low', but the primary trigger on COM III and SCR tractors is a sustained overvoltage condition exceeding 18 volts.

• 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 700 SCR
• Fendt 800 Vario (COM III)
• Fendt 800 SCR
• Fendt 900 Vario (COM III)
• Fendt 900 SCR

1. 1

   Start the engine and measure the voltage across the battery terminals and at the alternator output terminal to check for overcharging (>14.5V-15V).

2. 2

   Check the main power cables and ground straps between the alternator, the battery, and the A038 Central Electrical System for loose voltage sense wires or bad grounds.

3. 3

   Inspect the A038 Central Electrics box for melted fuses, burnt relays, or a scorched electrical smell, as 18+ volts can damage sensitive electronics.

1. 1

   Disconnect Power

   Disconnect the negative battery cable before performing any electrical repairs to prevent further shorting.

2. 2

   Replace the Alternator/Regulator

   If the diagnostic checks confirm overcharging, remove the drive belt and unbolt the faulty alternator. Replace it with a new unit (or replace the voltage regulator if it is serviceable separately on your specific Iskra/Mahle alternator).

3. 3

   Inspect/Replace the A038 ECU

   If the overvoltage condition fried the central electrical system, it will need to be replaced. The A038 Central Electrics box cannot be repaired if internally damaged; it must be replaced entirely.

4. 4

   Reassemble and Test

   Reinstall the alternator, tension the drive belt, and reconnect the battery. Start the tractor and verify with a multimeter that the charging voltage is stable at approximately 13.8V to 14.4V.

5. 5

   Clear Codes

   Use the tractor's Vario-Terminal or the FENDIAS diagnostic software to clear the stored 0F.1.1A fault code from the memory.