I bought a second-hand John Deere 4520 and after a while I started error code 74 on the panel.What is an error 74?
The error code 74 John Deere 4520 applies to the advance and reverse pedals.
To delete the codes, turn on the key and then press the advance pedal to the cover within 2 seconds and the release and do the same with the reverse pedal, the code must disappear unless the problem persists.
If so, you have to check the wiring of the potentiometers on each pedal and also check if one has moved [beaten out of range].
If none of the above is the case, then the solenoids of advance or retreat could be stuck, letting the tractor think that you have started it running, therefore there is no movement, these checks are not really the type “do it yousame “, so you may have to look for Deere’s help, I hope this helps.