Index: leahi_dialin/fp/filtration_purification.py
===================================================================
diff -u -rfc671af6d1a18c900812e68c42ca14da3280e4f1 -r5da31bc941a76297a8285323af9ff5d497ebe230
--- leahi_dialin/fp/filtration_purification.py	(.../filtration_purification.py)	(revision fc671af6d1a18c900812e68c42ca14da3280e4f1)
+++ leahi_dialin/fp/filtration_purification.py	(.../filtration_purification.py)	(revision 5da31bc941a76297a8285323af9ff5d497ebe230)
@@ -338,6 +338,49 @@
             can_interface = self.can_interface)
 
 
+    def cmd_fp_set_operation_sub_mode(self, new_mode: int = 0, new_sub_mode: int = 0) -> int:
+        """
+        Constructs and sends a set operation sub mode request command via CAN bus.
+        Constraints:
+            Must be logged into FP.
+            Transition from current to requested op sub mode must be legal.
+            NOTE: for POST the FP device shall be in Standby Mode
+
+        @param new_mode:  ID of operation mode to transition to
+        @param new_sub_mode:  ID of operation sub mode to transition to
+
+        @return: 1 if successful, zero otherwise
+        """
+        mode = integer_to_bytearray(new_mode)
+        sub_mode = integer_to_bytearray(new_sub_mode)
+        payload = mode + sub_mode
+ 
+        if new_mode == 0:
+            new_sub_mode_enum = fp_enum_repository.FPFaultStates(new_sub_mode)
+        elif new_mode == fp_enum_repository.FPOpModes.MODE_STAN.value:
+            new_sub_mode_enum = fp_enum_repository.FPStandbyStates(new_sub_mode)
+        elif new_mode == fp_enum_repository.FPOpModes.MODE_PRE_GENP.value:
+            new_sub_mode_enum = fp_enum_repository.FPPreGenPermeateStates(new_sub_mode)
+        elif new_mode == fp_enum_repository.FPOpModes.MODE_GENP.value:
+            new_sub_mode_enum = fp_enum_repository.FPGenPermeateStates(new_sub_mode)
+        elif new_mode == fp_enum_repository.FPOpModes.MODE_DPGP.value:
+            new_sub_mode_enum = fp_enum_repository.FPPreGenPDefStates(new_sub_mode)
+        elif new_mode == fp_enum_repository.FPOpModes.MODE_DEGP.value:
+            new_sub_mode_enum = fp_enum_repository.FPGenPermeateDefStates(new_sub_mode)
+        else:
+            new_sub_mode_enum = fp_enum_repository.FPOpModes.MODE_NLEG
+
+        return cmd_generic_override(
+            payload = payload,
+            reset = NO_RESET,
+            channel_id = DenaliChannels.dialin_to_fp_ch_id,
+            msg_id = MsgIds.MSG_ID_FP_SET_OP_SUB_MODE_REQUEST,
+            entity_name = 'FP Operation Sub Mode',
+            override_text = new_sub_mode_enum.name,
+            logger = self.logger,
+            can_interface = self.can_interface)
+
+
     def cmd_fp_software_reset_request(self) -> None:
         """
         Constructs and sends an FP software reset request via CAN bus.