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This instruction show you guide on how to solve AGCO tractor DTB DT205B trouble code D121.

The alternator voltage regulator voltage is too high (filtered battery signal) (X55).

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Possible causes

The filtered battery supply voltage is above 15.5 V

The alternator voltage regulator is faulty

The instrument panel voltage filter system is faulty



Consequences

There is a risk of overvoltage causing damage to the tractor electrical components.



D121 error code: diagnostic file
Check fuses F38 and F12.
Checking the voltage supplied by the two alternators

Test the voltage between terminal 1 of connector X192 or terminal 1 of connector X193 and the earth.



Note: 
For more information about the alternator test, refer to the workshop manual.

Erase any errors in the instrument panel and check that the error code does not re-appear.

Change the alternator voltage regulator. Repair the electrical fault if necessary.

Replace the instrument panel. The condenser inside the instrument panel may be faulty.


Note: 
Before replacing the instrument panel, check to make sure that the two voltage input terminals for the instrument panel are correct. Terminal 1 of connector X55 is connected to a + supply when the ignition is switched on. Terminal 68 of connector X55 is connected to a permanent + supply.


Carry out a test, while checking to ensure that the error code does not re-appear.