Encode DEF tank level as J1939 AT1T1 (PGN FEDF) frame
Encode DPF status as J1939 A1DPFC (PGN FEE5) frame
Encode NOx levels as J1939 EGR1 (PGN FEEF) frame
Encode SCR catalyst temperature (legacy method name for compatibility)
Get current state
Inject DEF (for testing)
Update aftertreatment state
Aftertreatment ECU virtual device