: To "enter" a control unit and see its specific codes, use the hazard warning light switch (on/off) or pull the turn signal lever toward you (the "flash-to-pass" position).
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. john deere d1a code
If wiring and sensor tests are inconclusive, if ECU diagnostics require dealer tools, or if you’re unsure about electrical testing. : To "enter" a control unit and see
: No diagnostic trouble codes are currently stored in that specific unit. if ECU diagnostics require dealer tools