diff --git a/awlsim/core/systemblocks/system_sfc.pxd.in b/awlsim/core/systemblocks/system_sfc.pxd.in
index 1ec1fe587..906cb9956 100644
--- a/awlsim/core/systemblocks/system_sfc.pxd.in
+++ b/awlsim/core/systemblocks/system_sfc.pxd.in
@@ -3,6 +3,7 @@ from awlsim.core.systemblocks.system_sfc_m4 cimport *
 from awlsim.core.systemblocks.system_sfc_m3 cimport *
 from awlsim.core.systemblocks.system_sfc_m2 cimport *
 from awlsim.core.systemblocks.system_sfc_m1 cimport *
+from awlsim.core.systemblocks.system_sfc_4 cimport *
 from awlsim.core.systemblocks.system_sfc_21 cimport *
 from awlsim.core.systemblocks.system_sfc_46 cimport *
 from awlsim.core.systemblocks.system_sfc_47 cimport *
diff --git a/awlsim/core/systemblocks/system_sfc.py b/awlsim/core/systemblocks/system_sfc.py
index e28fb709e..76d06e5f1 100644
--- a/awlsim/core/systemblocks/system_sfc.py
+++ b/awlsim/core/systemblocks/system_sfc.py
@@ -27,6 +27,7 @@
 from awlsim.core.systemblocks.system_sfc_m3 import * #+cimport
 from awlsim.core.systemblocks.system_sfc_m2 import * #+cimport
 from awlsim.core.systemblocks.system_sfc_m1 import * #+cimport
+from awlsim.core.systemblocks.system_sfc_4 import * #+cimport
 from awlsim.core.systemblocks.system_sfc_21 import * #+cimport
 from awlsim.core.systemblocks.system_sfc_46 import * #+cimport
 from awlsim.core.systemblocks.system_sfc_47 import * #+cimport
@@ -42,6 +43,7 @@
 	-2	: SFCm2,	# __REBOOT
 	-1	: SFCm1,	# __SFC_NOP
 
+	4	: SFC4,		# READ_RTM
 	21	: SFC21,	# FILL
 	46	: SFC46,	# STP
 	47	: SFC47,	# WAIT
diff --git a/awlsim/core/systemblocks/system_sfc_4.pxd.in b/awlsim/core/systemblocks/system_sfc_4.pxd.in
new file mode 100644
index 000000000..a3a9f92a8
--- /dev/null
+++ b/awlsim/core/systemblocks/system_sfc_4.pxd.in
@@ -0,0 +1,7 @@
+from awlsim.common.cython_support cimport *
+from awlsim.core.systemblocks.systemblocks cimport *
+
+cdef class SFC4(SFC):
+	cdef public list __meters
+
+	cpdef run(self)
diff --git a/awlsim/core/systemblocks/system_sfc_4.py b/awlsim/core/systemblocks/system_sfc_4.py
new file mode 100644
index 000000000..076e9fbe8
--- /dev/null
+++ b/awlsim/core/systemblocks/system_sfc_4.py
@@ -0,0 +1,87 @@
+# -*- coding: utf-8 -*-
+#
+# AWL simulator - SFCs
+#
+# Copyright 2026 QuackS7 contributors
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+#
+
+from __future__ import division, absolute_import, print_function, unicode_literals
+#from awlsim.common.cython_support cimport * #@cy
+from awlsim.common.compat import *
+
+from awlsim.common.exceptions import *
+from awlsim.common.util import *
+
+from awlsim.core.systemblocks.systemblocks import * #+cimport
+from awlsim.core.blockinterface import *
+from awlsim.core.memory import * #+cimport
+
+
+class SFC4(SFC): #+cdef
+	name = (4, "READ_RTM", "read runtime meter")
+
+	interfaceFields = {
+		BlockInterfaceField.FTYPE_IN	: (
+			BlockInterfaceField(name="NR", dataType="BYTE"),
+		),
+		BlockInterfaceField.FTYPE_OUT	: (
+			BlockInterfaceField(name="RET_VAL", dataType="INT"),
+			BlockInterfaceField(name="CQ", dataType="BOOL"),
+			BlockInterfaceField(name="CV", dataType="INT"),
+		),
+	}
+
+	def __init__(self, cpu):
+		SFC.__init__(self, cpu)
+		# 8 runtime meters, each (running: bool, hours: int).
+		# Until SFC 2 SET_RTM / SFC 3 CTRL_RTM are added, every meter
+		# reads back (False, 0) — the correct state for a CPU that has
+		# never started any runtime meter.
+		self.__meters = [[False, 0] for _ in range(8)]
+
+	def run(self): #+cpdef
+#@cy		cdef S7StatusWord s
+#@cy		cdef uint32_t nr
+
+		s = self.cpu.statusWord
+
+		nr = AwlMemoryObject_asScalar(
+			self.fetchInterfaceFieldByName("NR"))
+
+		if nr > 7:
+			# Siemens SFC_e §6.5 mandates flat specific code 0x8080 for
+			# NR out of range, not the general-code E_RPARM encoding.
+			# See docs/siemens/SFC_e (1).pdf §6.5 and rowlf's FLAG-B
+			# ruling (2026-04-17, user-ratified).
+			self.storeInterfaceFieldByName("RET_VAL",
+				make_AwlMemoryObject_fromScalar(0x8080, 16))
+			self.storeInterfaceFieldByName("CQ",
+				make_AwlMemoryObject_fromScalar(0, 1))
+			self.storeInterfaceFieldByName("CV",
+				make_AwlMemoryObject_fromScalar(0, 16))
+			s.BIE = 0
+			return
+
+		running, hours = self.__meters[nr]
+
+		self.storeInterfaceFieldByName("RET_VAL",
+			make_AwlMemoryObject_fromScalar(0, 16))
+		self.storeInterfaceFieldByName("CQ",
+			make_AwlMemoryObject_fromScalar(1 if running else 0, 1))
+		self.storeInterfaceFieldByName("CV",
+			make_AwlMemoryObject_fromScalar(hours & 0xFFFF, 16))
+		s.BIE = 1
diff --git a/tests/tc500_systemblocks/sfc/sfc4.awl b/tests/tc500_systemblocks/sfc/sfc4.awl
new file mode 100644
index 000000000..b9e201455
--- /dev/null
+++ b/tests/tc500_systemblocks/sfc/sfc4.awl
@@ -0,0 +1,85 @@
+ORGANIZATION_BLOCK OB 1
+	VAR_TEMP
+		NR_TMP		: BYTE;
+		RET_TMP		: INT;
+		CQ_TMP		: BOOL;
+		CV_TMP		: INT;
+	END_VAR
+BEGIN
+	// Test SFC 4: READ_RTM
+
+
+	// Valid meter number (0) on a fresh CPU: meter stopped, value 0.
+	L		B#16#00
+	T		#NR_TMP
+	CALL		SFC 4 (
+		NR	:= #NR_TMP,
+		RET_VAL	:= #RET_TMP,
+		CQ	:= #CQ_TMP,
+		CV	:= #CV_TMP,
+	)
+	__ASSERT==	__STW BIE,	1
+	L		#RET_TMP
+	__ASSERT==	__ACCU 1,	W#16#0000
+	L		#CV_TMP
+	__ASSERT==	__ACCU 1,	W#16#0000
+	U		#CQ_TMP
+	__ASSERT==	__STW VKE,	0
+
+
+	// Valid meter number (7, the maximum) - same expected state.
+	L		B#16#07
+	T		#NR_TMP
+	CALL		SFC 4 (
+		NR	:= #NR_TMP,
+		RET_VAL	:= #RET_TMP,
+		CQ	:= #CQ_TMP,
+		CV	:= #CV_TMP,
+	)
+	__ASSERT==	__STW BIE,	1
+	L		#RET_TMP
+	__ASSERT==	__ACCU 1,	W#16#0000
+	L		#CV_TMP
+	__ASSERT==	__ACCU 1,	W#16#0000
+	U		#CQ_TMP
+	__ASSERT==	__STW VKE,	0
+
+
+	// Invalid meter number (8): E_RPARM on parameter 1, BIE cleared.
+	L		B#16#08
+	T		#NR_TMP
+	CALL		SFC 4 (
+		NR	:= #NR_TMP,
+		RET_VAL	:= #RET_TMP,
+		CQ	:= #CQ_TMP,
+		CV	:= #CV_TMP,
+	)
+	__ASSERT==	__STW BIE,	0
+	L		#RET_TMP
+	__ASSERT==	__ACCU 1,	W#16#8080
+	L		#CV_TMP
+	__ASSERT==	__ACCU 1,	W#16#0000
+	U		#CQ_TMP
+	__ASSERT==	__STW VKE,	0
+
+
+	// Invalid meter number (255, max BYTE): same error path.
+	L		B#16#FF
+	T		#NR_TMP
+	CALL		SFC 4 (
+		NR	:= #NR_TMP,
+		RET_VAL	:= #RET_TMP,
+		CQ	:= #CQ_TMP,
+		CV	:= #CV_TMP,
+	)
+	__ASSERT==	__STW BIE,	0
+	L		#RET_TMP
+	__ASSERT==	__ACCU 1,	W#16#8080
+	L		#CV_TMP
+	__ASSERT==	__ACCU 1,	W#16#0000
+	U		#CQ_TMP
+	__ASSERT==	__STW VKE,	0
+
+
+	CALL SFC 46 // STOP CPU
+END_ORGANIZATION_BLOCK