How to Solve AGCO DTB DT205B Trouble Code D121 Error Code?

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.