diff --git a/engine/inc/com/centreon/engine/string.hh b/engine/inc/com/centreon/engine/string.hh
index 89c9bb5df44..7a47803cd05 100644
--- a/engine/inc/com/centreon/engine/string.hh
+++ b/engine/inc/com/centreon/engine/string.hh
@@ -29,7 +29,6 @@
 #include <sstream>
 #include <string>
 
-
 namespace com::centreon::engine {
 
 namespace string {
@@ -205,6 +204,8 @@ std::string& remove_thresholds(std::string& perfdata) noexcept;
 
 void unescape(char* buffer);
 
+void unescape(std::string& str);
+
 /**
  * @brief this class is a thread safe replacement for my_strtok
  * An instance is not thread safe but sevaral instances can be used in different
@@ -226,6 +227,6 @@ class c_strtok {
 
 }  // namespace string
 
-}
+}  // namespace com::centreon::engine
 
 #endif  // !CCE_MISC_STRING_HH
diff --git a/engine/src/command_manager.cc b/engine/src/command_manager.cc
index 1718b63442e..665fa498a71 100644
--- a/engine/src/command_manager.cc
+++ b/engine/src/command_manager.cc
@@ -137,6 +137,12 @@ int command_manager::process_passive_service_check(
   if (!found->second->passive_checks_enabled())
     return ERROR;
 
+  SPDLOG_LOGGER_DEBUG(runtime_logger,
+                      "process_passive_service_check check_time={}, "
+                      "host_name={}, service={}, return_code={}, output={}",
+                      check_time, host_name, svc_description, return_code,
+                      output);
+
   timeval tv;
   gettimeofday(&tv, nullptr);
 
diff --git a/engine/src/commands/commands.cc b/engine/src/commands/commands.cc
index ec6e7d53d1a..234d437038a 100644
--- a/engine/src/commands/commands.cc
+++ b/engine/src/commands/commands.cc
@@ -571,8 +571,8 @@ int cmd_process_service_check_result(int cmd [[maybe_unused]],
   ++ait;
 
   // replace \\n with \n
-  std::string output;
-  absl::CUnescape(*ait, &output);
+  std::string output(ait->data(), ait->size());
+  string::unescape(output);
 
   timeval tv;
   gettimeofday(&tv, nullptr);
diff --git a/engine/src/string.cc b/engine/src/string.cc
index 595ecb98b3a..b4cc09d9773 100644
--- a/engine/src/string.cc
+++ b/engine/src/string.cc
@@ -449,3 +449,16 @@ void string::unescape(char* buffer) {
     *buffer = 0;
   }
 }
+
+/**
+ * @brief  * @brief Unescape the string buffer. Works with \t, \n, \r and \\.
+ * The buffer is directly changed. No copy is made.
+ *
+ * @param str in out modified string
+ */
+void string::unescape(std::string& str) {
+  boost::replace_all(str, "\\n", "\n");
+  boost::replace_all(str, "\\r", "\r");
+  boost::replace_all(str, "\\t", "\t");
+  boost::replace_all(str, "\\\\", "\\");
+}
diff --git a/tests/broker-engine/external-commands2.robot b/tests/broker-engine/external-commands2.robot
index 65c6b7dc848..90d67fbcaec 100644
--- a/tests/broker-engine/external-commands2.robot
+++ b/tests/broker-engine/external-commands2.robot
@@ -1412,3 +1412,42 @@ BEHOSTCHECK
     Ctn Schedule Forced Host Check    host_1
     ${result}    Ctn Check Host Check With Timeout    host_1    30    ${VarRoot}/lib/centreon-engine/check.pl --id 0
     Should Be True    ${result}    hosts table not updated
+
+
+BE_BACKSLASH_CHECK_RESULT
+    [Documentation]    external command PROCESS_SERVICE_CHECK_RESULT with \:
+    [Tags]    broker    engine    services    extcmd   MON-51121
+    Ctn Config Engine    ${1}    ${50}    ${20}
+    Ctn Set Services Passive    ${0}    service_.*
+    Ctn Config Broker    rrd
+    Ctn Config Broker    central
+    Ctn Config Broker    module    ${1}
+    Ctn ConfigBBDO3    1
+    Ctn Config Broker Sql Output    central    unified_sql
+    Ctn Clear Retention
+    Ctn Broker Config Log    central    sql    debug
+    FOR    ${use_grpc}    IN RANGE    0    2
+        Log To Console    external command PROCESS_SERVICE_CHECK_RESULT  use_grpc=${use_grpc}
+        Ctn Clear Retention
+        ${start}    Get Current Date
+        Ctn Start Broker
+        Ctn Start engine
+        Ctn Wait For Engine To Be Ready    ${start}  ${1}
+
+        ${start}    Ctn Get Round Current Date
+        Ctn Process Service Check Result    host_1    service_1    0    output ok D: \\: Total: 1.205TB - Used: 1.203TB (100%) - Free: 2.541GB (0%) ${use_grpc}  config0  ${use_grpc}
+        
+        ${result}    Ctn Check Service Output Resource Status With Timeout
+        ...    host_1
+        ...    service_1
+        ...    35
+        ...    ${start}
+        ...    0
+        ...    HARD
+        ...    output ok D: \\: Total: 1.205TB - Used: 1.203TB (100%) - Free: 2.541GB (0%) ${use_grpc}
+        Should Be True    ${result}    resources table not updated
+
+
+        Ctn Stop engine
+        Ctn Kindly Stop Broker
+    END
diff --git a/tests/resources/Engine.py b/tests/resources/Engine.py
index e0562834e47..9d601ff85c6 100755
--- a/tests/resources/Engine.py
+++ b/tests/resources/Engine.py
@@ -2823,6 +2823,8 @@ def ctn_process_service_check_result(hst: str, svc: str, state: int, output: str
         0 on success.
     """
     if use_grpc > 0:
+        ts = Timestamp()
+        ts.GetCurrentTime()
         port = 50001 + int(config[6:])
         with grpc.insecure_channel(f"127.0.0.1:{port}") as channel:
             stub = engine_pb2_grpc.EngineStub(channel)
@@ -2830,10 +2832,10 @@ def ctn_process_service_check_result(hst: str, svc: str, state: int, output: str
                 for i in range(nb_check):
                     indexed_output = f"{output}_{i}"
                     stub.ProcessServiceCheckResult(engine_pb2.Check(
-                        host_name=hst, svc_desc=svc, output=indexed_output, code=state))
+                        host_name=hst, svc_desc=svc, check_time=ts, output=indexed_output, code=state))
             else:
                 stub.ProcessServiceCheckResult(engine_pb2.Check(
-                    host_name=hst, svc_desc=svc, output=output, code=state))
+                    host_name=hst, svc_desc=svc, check_time=ts, output=output, code=state))
 
     else:
         now = int(time.time())