diff --git a/litellm/proxy/common_request_processing.py b/litellm/proxy/common_request_processing.py
index 97f7d51970c..ff1f9a0e21c 100644
--- a/litellm/proxy/common_request_processing.py
+++ b/litellm/proxy/common_request_processing.py
@@ -239,11 +239,27 @@ async def _parse_event_data_for_error(event_line: Union[str, bytes]) -> Optional
                         # Not a valid integer string, treat as if no valid code was found for this check
                         pass
 
-                # Ensure error_code is a valid HTTP status code
+                # Return valid HTTP status codes as-is.
+                # Vendor-specific codes outside 100-599 (e.g. ZAI 1302, DashScope 4-digit
+                # throttle codes, or small integers like {"code": 2}) are mapped to
+                # 502 Bad Gateway so that create_streaming_response() can detect the error
+                # and the router failure/cooldown/fallback paths fire correctly. Without
+                # this mapping the error-bearing SSE chunk would be forwarded as normal
+                # content (200 OK) and the router would never know the deployment failed.
                 if error_code is not None and 100 <= error_code <= 599:
                     return error_code
-                elif error_code_raw is not None:  # Log if original code was present but not valid
-                    verbose_proxy_logger.warning(f"Error has invalid or non-convertible code: {error_code_raw}")
+                elif error_code is not None:
+                    verbose_proxy_logger.warning(
+                        f"Vendor SSE error code {error_code} is outside HTTP range; "
+                        f"mapping to 502 Bad Gateway for router error handling."
+                    )
+                    return 502
+                elif (
+                    error_code_raw is not None
+                ):  # Log if original code was present but not valid
+                    verbose_proxy_logger.warning(
+                        f"Error has invalid or non-convertible code: {error_code_raw}"
+                    )
         except (orjson.JSONDecodeError, json.JSONDecodeError):
             # not a known error chunk
             pass
diff --git a/tests/test_litellm/proxy/test_common_request_processing.py b/tests/test_litellm/proxy/test_common_request_processing.py
index 1d0dafed171..fbc6a0fc747 100644
--- a/tests/test_litellm/proxy/test_common_request_processing.py
+++ b/tests/test_litellm/proxy/test_common_request_processing.py
@@ -1117,12 +1117,12 @@ class TestCommonRequestProcessingHelpers:
             ),  # Invalid string code
             (
                 'data: {"error": {"code": 99, "message": "too low"}}',
-                None,
-            ),  # Integer code too low
+                502,
+            ),  # Integer code too low — below HTTP range, mapped to 502
             (
                 'data: {"error": {"code": 600, "message": "too high"}}',
-                None,
-            ),  # Integer code too high
+                502,
+            ),  # Integer code too high — above HTTP range, mapped to 502
             (
                 'data: {"id": "123", "content": "hello"}',
                 None,
diff --git a/tests/test_litellm/test_sse_vendor_error_codes.py b/tests/test_litellm/test_sse_vendor_error_codes.py
new file mode 100644
index 00000000000..89b8c72a68e
--- /dev/null
+++ b/tests/test_litellm/test_sse_vendor_error_codes.py
@@ -0,0 +1,125 @@
+"""
+Regression tests for SSE vendor error code mapping.
+
+Vendors like ZAI (ZhipuAI) and DashScope return error codes outside the
+standard HTTP 100-599 range in SSE chunks (e.g. 1302 for rate limits).
+_parse_event_data_for_error() must map these to 502 instead of returning None,
+so that create_streaming_response() can detect the error and the router's
+fallback/cooldown paths fire correctly.
+
+Fixes: https://github.com/BerriAI/litellm/issues/31284
+"""
+
+import json
+import pytest
+
+from litellm.proxy.common_request_processing import _parse_event_data_for_error
+
+
+class TestParseEventDataForError:
+    """Unit tests for _parse_event_data_for_error."""
+
+    @pytest.mark.asyncio
+    async def test_standard_http_error_code_returned_as_is(self):
+        """HTTP codes in 100-599 range are returned unchanged."""
+        chunk = 'data: {"error": {"code": 429, "message": "Rate limited"}}\n'
+        result = await _parse_event_data_for_error(chunk)
+        assert result == 429
+
+    @pytest.mark.asyncio
+    async def test_standard_http_500_returned_as_is(self):
+        chunk = 'data: {"error": {"code": 500, "message": "Server error"}}\n'
+        result = await _parse_event_data_for_error(chunk)
+        assert result == 500
+
+    @pytest.mark.asyncio
+    async def test_vendor_code_1302_mapped_to_502(self):
+        """ZAI rate-limit code 1302 should map to 502, not silently return None."""
+        chunk = 'data: {"error": {"code": 1302, "message": "\\u60a8\\u7684\\u8d26\\u6237\\u5df2\\u8fbe\\u5230\\u901f\\u7387\\u9650\\u5236"}}\n'
+        result = await _parse_event_data_for_error(chunk)
+        assert (
+            result == 502
+        ), "Vendor code 1302 must be mapped to 502 so the router detects the error"
+
+    @pytest.mark.asyncio
+    async def test_vendor_code_1305_mapped_to_502(self):
+        """ZAI 1305 (quota exceeded) should map to 502."""
+        chunk = 'data: {"error": {"code": 1305, "message": "Quota exceeded"}}\n'
+        result = await _parse_event_data_for_error(chunk)
+        assert result == 502
+
+    @pytest.mark.asyncio
+    async def test_vendor_code_4digit_mapped_to_502(self):
+        """DashScope-style 4-digit throttle codes (e.g. 4001) should map to 502."""
+        chunk = 'data: {"error": {"code": 4001, "message": "Throttled"}}\n'
+        result = await _parse_event_data_for_error(chunk)
+        assert result == 502
+
+    @pytest.mark.asyncio
+    async def test_no_error_field_returns_none(self):
+        """Normal content chunks (no 'error' key) return None."""
+        chunk = 'data: {"choices": [{"delta": {"content": "hello"}}]}\n'
+        result = await _parse_event_data_for_error(chunk)
+        assert result is None
+
+    @pytest.mark.asyncio
+    async def test_done_sentinel_returns_none(self):
+        """[DONE] sentinel returns None."""
+        result = await _parse_event_data_for_error("data: [DONE]\n")
+        assert result is None
+
+    @pytest.mark.asyncio
+    async def test_empty_data_returns_none(self):
+        result = await _parse_event_data_for_error("data: \n")
+        assert result is None
+
+    @pytest.mark.asyncio
+    async def test_string_vendor_code_mapped_to_502(self):
+        """Vendor codes that arrive as strings and are >= 600 still map to 502."""
+        chunk = 'data: {"error": {"code": "1302", "message": "Rate limit"}}\n'
+        result = await _parse_event_data_for_error(chunk)
+        assert result == 502
+
+    @pytest.mark.asyncio
+    async def test_string_http_code_returned_as_is(self):
+        """String HTTP code in 100-599 range is returned as the integer value."""
+        chunk = 'data: {"error": {"code": "429", "message": "Rate limit"}}\n'
+        result = await _parse_event_data_for_error(chunk)
+        assert result == 429
+
+    @pytest.mark.asyncio
+    async def test_bytes_input_vendor_code_mapped_to_502(self):
+        """Byte-string input with vendor code >= 600 maps to 502."""
+        chunk = b'data: {"error": {"code": 1302, "message": "Rate limit"}}\n'
+        result = await _parse_event_data_for_error(chunk)
+        assert result == 502
+
+    @pytest.mark.asyncio
+    async def test_error_with_none_code_returns_none(self):
+        """error object present but 'code' is absent — return None."""
+        chunk = 'data: {"error": {"message": "Something went wrong"}}\n'
+        result = await _parse_event_data_for_error(chunk)
+        assert result is None
+
+    @pytest.mark.asyncio
+    async def test_small_vendor_code_2_mapped_to_502(self):
+        """Small integer vendor codes (< 100) must map to 502, not silently return None."""
+        chunk = 'data: {"error": {"code": 2, "message": "Unknown error"}}\n'
+        result = await _parse_event_data_for_error(chunk)
+        assert (
+            result == 502
+        ), "Vendor code 2 must be mapped to 502 so the router detects the error"
+
+    @pytest.mark.asyncio
+    async def test_vendor_code_zero_mapped_to_502(self):
+        """Code 0 is outside HTTP range and must map to 502."""
+        chunk = 'data: {"error": {"code": 0, "message": "Connection reset"}}\n'
+        result = await _parse_event_data_for_error(chunk)
+        assert result == 502
+
+    @pytest.mark.asyncio
+    async def test_vendor_code_99_mapped_to_502(self):
+        """Code 99 (below HTTP minimum of 100) must map to 502."""
+        chunk = 'data: {"error": {"code": 99, "message": "Internal code"}}\n'
+        result = await _parse_event_data_for_error(chunk)
+        assert result == 502