diff --git a/src/diffusers/commands/custom_blocks.py b/src/diffusers/commands/custom_blocks.py
index 43d9ea8857..07fca44678 100644
--- a/src/diffusers/commands/custom_blocks.py
+++ b/src/diffusers/commands/custom_blocks.py
@@ -27,7 +27,7 @@ from ..utils import logging
 from . import BaseDiffusersCLICommand
 
 
-EXPECTED_PARENT_CLASSES = ["ModularPipelineBlocks"]
+EXPECTED_PARENT_CLASSES = ["PipelineBlock"]
 CONFIG = "config.json"
 
 
diff --git a/src/diffusers/modular_pipelines/modular_pipeline.py b/src/diffusers/modular_pipelines/modular_pipeline.py
index b99478cb58..6607ea1efe 100644
--- a/src/diffusers/modular_pipelines/modular_pipeline.py
+++ b/src/diffusers/modular_pipelines/modular_pipeline.py
@@ -351,6 +351,7 @@ class ModularPipelineBlocks(ConfigMixin, PushToHubMixin):
             "token",
         ]
         hub_kwargs = {name: kwargs.pop(name) for name in hub_kwargs_names if name in kwargs}
+        hub_kwargs.update({"trust_remote_code": trust_remote_code})
 
         config = cls.load_config(pretrained_model_name_or_path)
         has_remote_code = "auto_map" in config and cls.__name__ in config["auto_map"]
@@ -358,7 +359,9 @@ class ModularPipelineBlocks(ConfigMixin, PushToHubMixin):
             trust_remote_code, pretrained_model_name_or_path, has_remote_code
         )
         if not (has_remote_code and trust_remote_code):
-            raise ValueError("TODO")
+            raise ValueError(
+                "Selected model repository does not happear to have any custom code or does not have a valid `config.json` file."
+            )
 
         class_ref = config["auto_map"][cls.__name__]
         module_file, class_name = class_ref.split(".")
@@ -367,7 +370,6 @@ class ModularPipelineBlocks(ConfigMixin, PushToHubMixin):
             pretrained_model_name_or_path,
             module_file=module_file,
             class_name=class_name,
-            is_modular=True,
             **hub_kwargs,
             **kwargs,
         )
@@ -384,10 +386,39 @@ class ModularPipelineBlocks(ConfigMixin, PushToHubMixin):
 
         full_mod = type(self).__module__
         module = full_mod.rsplit(".", 1)[-1].replace("__dynamic__", "")
-        parent_module = self.save_pretrained.__func__.__qualname__.split(".", 1)[0]
+        parent_module = self.__class__.__bases__[0].__name__
         auto_map = {f"{parent_module}": f"{module}.{cls_name}"}
 
         self.register_to_config(auto_map=auto_map)
+
+        _component_specs = {spec.name: deepcopy(spec) for spec in self.expected_components}
+        _config_specs = {spec.name: deepcopy(spec) for spec in self.expected_configs}
+
+        register_components_dict = {}
+        for name, component_spec in _component_specs.items():
+            if component_spec.type_hint is not None:
+                lib_name, cls_name = _fetch_class_library_tuple(component_spec.type_hint)
+            else:
+                lib_name = cls_name = None
+            load_spec_dict = {k: getattr(component_spec, k) for k in component_spec.loading_fields()}
+
+            # Since ModularPipelineBlocks can never have loaded components we set
+            # first two fields in the config dict to None
+            register_components_dict[name] = (
+                None,
+                None,
+                {
+                    "type_hint": (lib_name, cls_name),
+                    **load_spec_dict,
+                },
+            )
+        self.register_to_config(**register_components_dict)
+
+        default_configs = {}
+        for name, config_spec in _config_specs.items():
+            default_configs[name] = config_spec.default
+        self.register_to_config(**default_configs)
+
         self.save_config(save_directory=save_directory, push_to_hub=push_to_hub, **kwargs)
         config = dict(self.config)
         self._internal_dict = FrozenDict(config)
diff --git a/src/diffusers/modular_pipelines/modular_pipeline_utils.py b/src/diffusers/modular_pipelines/modular_pipeline_utils.py
index 4fac5ef4f2..b63925df26 100644
--- a/src/diffusers/modular_pipelines/modular_pipeline_utils.py
+++ b/src/diffusers/modular_pipelines/modular_pipeline_utils.py
@@ -93,7 +93,7 @@ class ComponentSpec:
     config: Optional[FrozenDict] = None
     # YiYi Notes: should we change it to pretrained_model_name_or_path for consistency? a bit long for a field name
     repo: Optional[Union[str, List[str]]] = field(default=None, metadata={"loading": True})
-    subfolder: Optional[str] = field(default=None, metadata={"loading": True})
+    subfolder: Optional[str] = field(default="", metadata={"loading": True})
     variant: Optional[str] = field(default=None, metadata={"loading": True})
     revision: Optional[str] = field(default=None, metadata={"loading": True})
     default_creation_method: Literal["from_config", "from_pretrained"] = "from_pretrained"