Corroded terminals or a short in the diagnostic wiring can trigger the mode. A known John Deere service solution (DTAC #71449) addresses tractors entering this mode on their own due to grounding issues.
On many models (like the 6000 or 7000 series), there is a specific slot in the fuse box for diagnostics. If a fuse is in this slot, the tractor defaults to "d1A" mode and may not move. john deere d1a code
This is not a traditional "error code" indicating a broken part; rather, it is a status indicator that the system is ready for troubleshooting or viewing specific diagnostic data. What Does the d1A Code Mean? Corroded terminals or a short in the diagnostic