diff --git a/Geometry/ForwardGeometry/src/ZdcTopology.cc b/Geometry/ForwardGeometry/src/ZdcTopology.cc
index e0b92ccff8ae3..83a704f3382ee 100644
--- a/Geometry/ForwardGeometry/src/ZdcTopology.cc
+++ b/Geometry/ForwardGeometry/src/ZdcTopology.cc
@@ -22,7 +22,7 @@ ZdcTopology::ZdcTopology(const HcalDDDRecConstants* hcons)
       firstRPDModule_(1),
       lastRPDModule_(HcalZDCDetId::kDepRPD) {
   mode_ = (HcalTopologyMode::Mode)(hcons_->getTopoMode());
-  excludeRPD_ = (mode_ < HcalTopologyMode::Mode::Run3);
+  excludeRPD_ = ((mode_ != HcalTopologyMode::Mode::Run3) && (mode_ != HcalTopologyMode::Mode::Run4));
   edm::LogVerbatim("ForwardGeom") << "ZdcTopology : Mode " << mode_ << ":" << HcalTopologyMode::Mode::Run3
                                   << " ExcludeRPD " << excludeRPD_;
 }
diff --git a/Geometry/ForwardGeometry/test/BuildFile.xml b/Geometry/ForwardGeometry/test/BuildFile.xml
index 5021eae6332f0..5cc59f6aa5657 100644
--- a/Geometry/ForwardGeometry/test/BuildFile.xml
+++ b/Geometry/ForwardGeometry/test/BuildFile.xml
@@ -1,5 +1,7 @@
+<use name="DataFormats/HcalDetId"/>
 <use name="DataFormats/ForwardDetId"/>
 <use name="Geometry/HGCalGeometry"/>
+<use name="Geometry/ForwardGeometry"/>
 <use name="Geometry/Records"/>
 <use name="CoralBase"/>
 <flags EDM_PLUGIN="1"/>
diff --git a/Geometry/ForwardGeometry/test/ZdcTopologyTester.cc b/Geometry/ForwardGeometry/test/ZdcTopologyTester.cc
new file mode 100644
index 0000000000000..27a232418cfd4
--- /dev/null
+++ b/Geometry/ForwardGeometry/test/ZdcTopologyTester.cc
@@ -0,0 +1,137 @@
+#include <iostream>
+#include <sstream>
+#include <string>
+#include <vector>
+
+#include "FWCore/Framework/interface/Frameworkfwd.h"
+#include "FWCore/Framework/interface/one/EDAnalyzer.h"
+#include "FWCore/Framework/interface/Event.h"
+#include "FWCore/Framework/interface/EventSetup.h"
+#include "FWCore/Framework/interface/ESTransientHandle.h"
+#include "FWCore/Framework/interface/MakerMacros.h"
+#include "FWCore/MessageLogger/interface/MessageLogger.h"
+#include "FWCore/ParameterSet/interface/ParameterSet.h"
+#include "FWCore/ParameterSet/interface/ConfigurationDescriptions.h"
+
+#include "Geometry/Records/interface/HcalRecNumberingRecord.h"
+#include "Geometry/ForwardGeometry/interface/ZdcTopology.h"
+#include "DataFormats/HcalDetId/interface/HcalZDCDetId.h"
+
+class ZdcTopologyTester : public edm::one::EDAnalyzer<edm::one::WatchRuns> {
+public:
+  explicit ZdcTopologyTester(const edm::ParameterSet&);
+
+  static void fillDescriptions(edm::ConfigurationDescriptions& descriptions);
+
+private:
+  void analyze(edm::Event const&, edm::EventSetup const&) override;
+  void beginJob() override {}
+  void beginRun(edm::Run const&, edm::EventSetup const&) override {}
+  void endRun(edm::Run const&, edm::EventSetup const&) override {}
+  void doTest(const ZdcTopology& topology);
+
+  // ----------member data ---------------------------
+  const edm::ESGetToken<ZdcTopology, HcalRecNumberingRecord> tokTopo_;
+};
+
+ZdcTopologyTester::ZdcTopologyTester(const edm::ParameterSet&)
+    : tokTopo_{esConsumes<ZdcTopology, HcalRecNumberingRecord>(edm::ESInputTag{})} {}
+
+void ZdcTopologyTester::fillDescriptions(edm::ConfigurationDescriptions& descriptions) {
+  edm::ParameterSetDescription desc;
+  desc.setUnknown();
+  descriptions.add("zdcTopologyTester", desc);
+}
+
+void ZdcTopologyTester::analyze(edm::Event const&, edm::EventSetup const& iSetup) { doTest(iSetup.getData(tokTopo_)); }
+
+void ZdcTopologyTester::doTest(const ZdcTopology& topology) {
+  // Total number of valid cells
+  for (int idet = 0; idet < 4; idet++) {
+    int ndet(0);
+    std::string det = "EM";
+    HcalZDCDetId::Section section = HcalZDCDetId::EM;
+    if (idet == 1) {
+      det = "HAD";
+      section = HcalZDCDetId::HAD;
+    } else if (idet == 2) {
+      det ="LUM";
+      section = HcalZDCDetId::LUM;
+    } else if (idet == 3) {
+      det = "RPD";
+      section = HcalZDCDetId::RPD;
+    }
+    for (int depth = 1; depth <= HcalZDCDetId::kDepTot; ++depth) {
+      for (int zside = 0; zside <= 1; ++zside) {
+	bool forward = (zside == 0) ? true : false;
+	const HcalZDCDetId id(section, forward, depth);
+	if (topology.valid(id))
+	  ++ndet;
+      }
+    }
+    edm::LogVerbatim("HCalGeom") << "Number of valid cells in " << det << ": " << ndet;
+  }
+  
+  // First test on movements along eta/phi directions
+  edm::LogVerbatim("HCalGeom") << "\nTest on movements along transverse/longiudnal directions"
+                               << "\n========================================================";
+  for (int idet = 0; idet < 4; idet++) {
+    HcalZDCDetId::Section section = HcalZDCDetId::EM;
+    if (idet == 1)
+      section = HcalZDCDetId::HAD;
+    else if (idet == 2)
+      section = HcalZDCDetId::LUM;
+    else if (idet == 3)
+      section = HcalZDCDetId::RPD;
+    for (int depth = 1; depth <= HcalZDCDetId::kDepTot; ++depth) {
+      for (int zside = 0; zside <= 1; ++zside) {
+	bool forward = (zside == 0) ? true : false;
+	const HcalZDCDetId id(section, forward, depth);
+	if (topology.valid(id)) {
+            std::vector<DetId> idT = topology.transverse(id);
+            std::vector<DetId> idL = topology.longitudinal(id);
+            edm::LogVerbatim("HCalGeom") << "Neighbours for : Tower " << id;
+            std::ostringstream st1;
+            st1 << "          " << idT.size() << " sets transverse:";
+            for (auto& i : idT)
+              st1 << " " << (HcalZDCDetId)(i());
+            edm::LogVerbatim("HCalGeom") << st1.str();
+            std::ostringstream st2;
+            st2 << "          " << idL.size() << " sets along Longitunal:";
+            for (auto& i : idL)
+              st2 << " " << (HcalZDCDetId)(i());
+            edm::LogVerbatim("HCalGeom") << st2.str();
+	}
+      }
+    }
+  }
+
+  // Check on Dense Index
+  edm::LogVerbatim("HCalGeom") << "\nCheck on Dense Index"
+                               << "\n=====================";
+  for (int idet = 0; idet < 4; idet++) {
+    HcalZDCDetId::Section section = HcalZDCDetId::EM;
+    if (idet == 1)
+      section = HcalZDCDetId::HAD;
+    else if (idet == 2)
+      section = HcalZDCDetId::LUM;
+    else if (idet == 3)
+      section = HcalZDCDetId::RPD;
+    for (int depth = 1; depth <= HcalZDCDetId::kDepTot; ++depth) {
+      for (int zside = 0; zside <= 1; ++zside) {
+	bool forward = (zside == 0) ? true : false;
+	HcalZDCDetId cell(section, forward, depth);
+	if (topology.valid(cell)) {
+	  unsigned int dense = topology.detId2DenseIndex(DetId(cell));
+	  DetId id = topology.denseId2detId(dense);
+	  std::string cherr = (cell.rawId() != id.rawId()) ? " **** ERROR *****" : "";
+	  edm::LogVerbatim("HCalGeom") << cell << " Dense " << std::hex << dense << std::dec << " o/p "
+				       << HcalZDCDetId(id) << cherr;
+        }
+      }
+    }
+  }
+}
+
+//define this as a plug-in
+DEFINE_FWK_MODULE(ZdcTopologyTester);
diff --git a/Geometry/ForwardGeometry/test/testZdcTopology_cfg.py b/Geometry/ForwardGeometry/test/testZdcTopology_cfg.py
new file mode 100644
index 0000000000000..c8adad4127255
--- /dev/null
+++ b/Geometry/ForwardGeometry/test/testZdcTopology_cfg.py
@@ -0,0 +1,67 @@
+###############################################################################
+# Way to use this:
+#   cmsRun testZdcTopology_cfg.py type=2024
+#
+#   Options for type 2021, 2023, 2024
+#
+###############################################################################
+import FWCore.ParameterSet.Config as cms
+import os, sys, imp, re
+import FWCore.ParameterSet.VarParsing as VarParsing
+
+####################################################################
+### SETUP OPTIONS 
+options = VarParsing.VarParsing('standard')
+options.register('type',
+                 "2024",
+                  VarParsing.VarParsing.multiplicity.singleton,
+                  VarParsing.VarParsing.varType.string,
+                  "type of operations:2021, 2023, 2024")
+
+### get and parse the command line arguments
+options.parseArguments()
+
+geomFile = "Configuration.Geometry.GeometryExtended" + options.type + "Reco_cff"
+
+print(options)
+print("Geometry file: ", geomFile)
+
+####################################################################
+# Use the options
+
+from Configuration.Eras.Era_Run3_DDD_cff import Run3_DDD
+process = cms.Process('TestZdcTopology',Run3_DDD)
+
+process.load("SimGeneral.HepPDTESSource.pdt_cfi")
+process.load(geomFile)
+process.load("Geometry.ForwardGeometry.zdcTopologyTester_cfi")
+process.load('FWCore.MessageService.MessageLogger_cfi')
+
+if hasattr(process,'MessageLogger'):
+    process.MessageLogger.HCalGeom=dict()
+
+process.load("IOMC.RandomEngine.IOMC_cff")
+process.RandomNumberGeneratorService.generator.initialSeed = 456789
+
+process.source = cms.Source("EmptySource")
+
+process.generator = cms.EDProducer("FlatRandomEGunProducer",
+    PGunParameters = cms.PSet(
+        PartID = cms.vint32(14),
+        MinEta = cms.double(-3.5),
+        MaxEta = cms.double(3.5),
+        MinPhi = cms.double(-3.14159265359),
+        MaxPhi = cms.double(3.14159265359),
+        MinE   = cms.double(9.99),
+        MaxE   = cms.double(10.01)
+    ),
+    AddAntiParticle = cms.bool(False),
+    Verbosity       = cms.untracked.int32(0),
+    firstRun        = cms.untracked.uint32(1)
+)
+
+process.maxEvents = cms.untracked.PSet(
+    input = cms.untracked.int32(1)
+)
+
+process.p1 = cms.Path(process.generator*process.zdcTopologyTester)