Index: leahi_dialin/common/fp_defs.py
===================================================================
diff -u -rbfc16802b17ae93c46555ff4fbf9ee7ddcb05523 -r57aed15d5b38f236deaea49daba706ce352162d2
--- leahi_dialin/common/fp_defs.py	(.../fp_defs.py)	(revision bfc16802b17ae93c46555ff4fbf9ee7ddcb05523)
+++ leahi_dialin/common/fp_defs.py	(.../fp_defs.py)	(revision 57aed15d5b38f236deaea49daba706ce352162d2)
@@ -131,7 +131,7 @@
     FP_PRE_GENP_CONCENTRATE_FLUSH   = 3                         # FP Pre Gen Permeate Concentrate Flush State
     FP_PRE_GENP_VERIFY_WATER        = 4                         # FP Pre Gen Permeate Verify Water State
     FP_PRE_GENP_PAUSED              = 5                         # FP Pre Gen Permeate Paused State
-    NUM_OF_FP_PRE_GENP_MODE_STATES  = 7                         # Number of Pre-Gen Permeate mode states
+    NUM_OF_FP_PRE_GENP_MODE_STATES  = 6                         # Number of Pre-Gen Permeate mode states
 
 FPPreGenPermeateStates._str_list = {
     # Official Name :               Accepted strings
Index: leahi_dialin/common/msg_ids.py
===================================================================
diff -u -r010ae5ad615ce1206e2ce2996e5ff4e945e82ebc -r57aed15d5b38f236deaea49daba706ce352162d2
--- leahi_dialin/common/msg_ids.py	(.../msg_ids.py)	(revision 010ae5ad615ce1206e2ce2996e5ff4e945e82ebc)
+++ leahi_dialin/common/msg_ids.py	(.../msg_ids.py)	(revision 57aed15d5b38f236deaea49daba706ce352162d2)
@@ -429,6 +429,7 @@
     MSG_ID_FP_DEF_GEN_PUBLISH_INTERVAL_OVERRIDE_REQUEST = 0xB043
     MSG_ID_FP_DEF_STATUS_REQUEST = 0xB044
     MSG_ID_FP_DEF_STATUS_RESPONSE = 0xB045
+    MSG_ID_FP_SET_OP_SUB_MODE_REQUEST = 0xB046
 
     MSG_ID_FP_CONDUCTIVITY_SENSOR_RESISTANCE_OVERRIDE_REQUEST = 0xB100
 
Index: leahi_dialin/fp/filtration_purification.py
===================================================================
diff -u -r20c821bd230fc7689a0275a2918981669ff5cc19 -r57aed15d5b38f236deaea49daba706ce352162d2
--- leahi_dialin/fp/filtration_purification.py	(.../filtration_purification.py)	(revision 20c821bd230fc7689a0275a2918981669ff5cc19)
+++ leahi_dialin/fp/filtration_purification.py	(.../filtration_purification.py)	(revision 57aed15d5b38f236deaea49daba706ce352162d2)
@@ -345,6 +345,46 @@
             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 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 self.fp_operation_mode == 0:
+            new_mode_enum = fp_enum_repository.FPFaultStates(new_mode)
+        elif self.fp_operation_mode == fp_enum_repository.FPOpModes.MODE_PRE_GENP.value:
+            new_mode_enum = fp_enum_repository.FPPreGenPermeateStates(new_mode)
+        elif self.fp_operation_mode == fp_enum_repository.FPOpModes.MODE_GENP.value:
+            new_mode_enum = fp_enum_repository.FPGenPermeateStates(new_mode)
+        elif self.fp_operation_mode == fp_enum_repository.FPOpModes.MODE_DPGP.value:
+            new_mode_enum = fp_enum_repository.FPPreGenPDefStates(new_mode)
+        elif self.fp_operation_mode == fp_enum_repository.FPOpModes.MODE_DEGP.value:
+            new_mode_enum = fp_enum_repository.FPGenPermeateDefStates(new_mode)
+        else:
+            new_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_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.