diff --git a/.github/release-trigger.yml b/.github/release-trigger.yml
index 53b5d8c5..f57ef988 100644
--- a/.github/release-trigger.yml
+++ b/.github/release-trigger.yml
@@ -13,3 +13,4 @@
 # limitations under the License.
 
 enabled: true
+multiScmName: alloydb-python-connector
diff --git a/.github/workflows/codeql.yaml b/.github/workflows/codeql.yaml
index 6d75239d..524c1abd 100644
--- a/.github/workflows/codeql.yaml
+++ b/.github/workflows/codeql.yaml
@@ -49,16 +49,16 @@ jobs:
 
     # Initializes the CodeQL tools for scanning.
     - name: Initialize CodeQL
-      uses: github/codeql-action/init@396bb3e45325a47dd9ef434068033c6d5bb0d11a # v3.27.3
+      uses: github/codeql-action/init@babb554ede22fd5605947329c4d04d8e7a0b8155 # v3.27.7
       with:
         languages: ${{ matrix.language }}
 
     # Autobuild attempts to build any compiled languages  (C/C++, C#, Go, or Java).
     # If this step fails, then you should remove it and run the build manually
     - name: Autobuild
-      uses: github/codeql-action/autobuild@396bb3e45325a47dd9ef434068033c6d5bb0d11a # v3.27.3
+      uses: github/codeql-action/autobuild@babb554ede22fd5605947329c4d04d8e7a0b8155 # v3.27.7
 
     - name: Perform CodeQL Analysis
-      uses: github/codeql-action/analyze@396bb3e45325a47dd9ef434068033c6d5bb0d11a # v3.27.3
+      uses: github/codeql-action/analyze@babb554ede22fd5605947329c4d04d8e7a0b8155 # v3.27.7
       with:
         category: "/language:${{matrix.language}}"
diff --git a/.github/workflows/scorecard.yaml b/.github/workflows/scorecard.yaml
index 2bc12c98..3185b9be 100644
--- a/.github/workflows/scorecard.yaml
+++ b/.github/workflows/scorecard.yaml
@@ -65,6 +65,6 @@ jobs:
 
       # Upload the results to GitHub's code scanning dashboard.
       - name: "Upload to code-scanning"
-        uses: github/codeql-action/upload-sarif@396bb3e45325a47dd9ef434068033c6d5bb0d11a # v3.27.3
+        uses: github/codeql-action/upload-sarif@babb554ede22fd5605947329c4d04d8e7a0b8155 # v3.27.7
         with:
           sarif_file: resultsFiltered.sarif
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 16240d16..0eedcbe8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,13 @@
 # Changelog
 
+## [1.6.0](https://github.com/GoogleCloudPlatform/alloydb-python-connector/compare/v1.5.0...v1.6.0) (2024-12-10)
+
+
+### Features
+
+* improve aiohttp client error messages ([#400](https://github.com/GoogleCloudPlatform/alloydb-python-connector/issues/400)) ([58ef2d2](https://github.com/GoogleCloudPlatform/alloydb-python-connector/commit/58ef2d2538e3a332defefa15d19b1384db9027b1))
+* invalidate cache on bad connection info and failed IP lookup ([#389](https://github.com/GoogleCloudPlatform/alloydb-python-connector/issues/389)) ([e8fbbdf](https://github.com/GoogleCloudPlatform/alloydb-python-connector/commit/e8fbbdf80d8aa5f0df2605a779edff631e5f5a2c))
+
 ## [1.5.0](https://github.com/GoogleCloudPlatform/alloydb-python-connector/compare/v1.4.0...v1.5.0) (2024-11-12)
 
 
diff --git a/README.md b/README.md
index 861a043c..c1656027 100644
--- a/README.md
+++ b/README.md
@@ -8,12 +8,14 @@
 
 [![CI][ci-badge]][ci-build]
 [![pypi][pypi-badge]][pypi-docs]
+[![pypi][pypi-downloads]][pypi-docs]
 [![python][python-versions]][pypi-docs]
 
 [ci-badge]: https://github.com/GoogleCloudPlatform/alloydb-python-connector/actions/workflows/tests.yaml/badge.svg?event=push
 [ci-build]: https://github.com/GoogleCloudPlatform/alloydb-python-connector/actions/workflows/tests.yaml?query=event%3Apush+branch%3Amain
 [pypi-badge]: https://img.shields.io/pypi/v/google-cloud-alloydb-connector
 [pypi-docs]: https://pypi.org/project/google-cloud-alloydb-connector
+[pypi-downloads]: https://img.shields.io/pypi/dm/google-cloud-alloydb-connector
 [python-versions]: https://img.shields.io/pypi/pyversions/google-cloud-alloydb-connector
 
 The _AlloyDB Python Connector_ is an [AlloyDB](https://cloud.google.com/alloydb)
diff --git a/google/cloud/alloydb/connector/async_connector.py b/google/cloud/alloydb/connector/async_connector.py
index d1961a6f..fba74887 100644
--- a/google/cloud/alloydb/connector/async_connector.py
+++ b/google/cloud/alloydb/connector/async_connector.py
@@ -177,8 +177,14 @@ async def connect(
         # if ip_type is str, convert to IPTypes enum
         if isinstance(ip_type, str):
             ip_type = IPTypes(ip_type.upper())
-        conn_info = await cache.connect_info()
-        ip_address = conn_info.get_preferred_ip(ip_type)
+        try:
+            conn_info = await cache.connect_info()
+            ip_address = conn_info.get_preferred_ip(ip_type)
+        except Exception:
+            # with an error from AlloyDB API call or IP type, invalidate the
+            # cache and re-raise the error
+            await self._remove_cached(instance_uri)
+            raise
         logger.debug(f"['{instance_uri}']: Connecting to {ip_address}:5433")
 
         # callable to be used for auto IAM authn
@@ -202,6 +208,15 @@ def get_authentication_token() -> str:
             await cache.force_refresh()
             raise
 
+    async def _remove_cached(self, instance_uri: str) -> None:
+        """Stops all background refreshes and deletes the connection
+        info cache from the map of caches.
+        """
+        logger.debug(f"['{instance_uri}']: Removing connection info from cache")
+        # remove cache from stored caches and close it
+        cache = self._cache.pop(instance_uri)
+        await cache.close()
+
     async def __aenter__(self) -> Any:
         """Enter async context manager by returning Connector object"""
         return self
diff --git a/google/cloud/alloydb/connector/client.py b/google/cloud/alloydb/connector/client.py
index 6edb9ee4..59e923a4 100644
--- a/google/cloud/alloydb/connector/client.py
+++ b/google/cloud/alloydb/connector/client.py
@@ -124,8 +124,20 @@ async def _get_metadata(
 
         url = f"{self._alloydb_api_endpoint}/{API_VERSION}/projects/{project}/locations/{region}/clusters/{cluster}/instances/{name}/connectionInfo"
 
-        resp = await self._client.get(url, headers=headers, raise_for_status=True)
-        resp_dict = await resp.json()
+        resp = await self._client.get(url, headers=headers)
+        # try to get response json for better error message
+        try:
+            resp_dict = await resp.json()
+            if resp.status >= 400:
+                # if detailed error message is in json response, use as error message
+                message = resp_dict.get("error", {}).get("message")
+                if message:
+                    resp.reason = message
+        # skip, raise_for_status will catch all errors in finally block
+        except Exception:
+            pass
+        finally:
+            resp.raise_for_status()
 
         # Remove trailing period from PSC DNS name.
         psc_dns = resp_dict.get("pscDnsName")
@@ -175,10 +187,20 @@ async def _get_client_certificate(
             "useMetadataExchange": self._use_metadata,
         }
 
-        resp = await self._client.post(
-            url, headers=headers, json=data, raise_for_status=True
-        )
-        resp_dict = await resp.json()
+        resp = await self._client.post(url, headers=headers, json=data)
+        # try to get response json for better error message
+        try:
+            resp_dict = await resp.json()
+            if resp.status >= 400:
+                # if detailed error message is in json response, use as error message
+                message = resp_dict.get("error", {}).get("message")
+                if message:
+                    resp.reason = message
+        # skip, raise_for_status will catch all errors in finally block
+        except Exception:
+            pass
+        finally:
+            resp.raise_for_status()
 
         return (resp_dict["caCert"], resp_dict["pemCertificateChain"])
 
diff --git a/google/cloud/alloydb/connector/connector.py b/google/cloud/alloydb/connector/connector.py
index 2d1bfee2..c4ad2997 100644
--- a/google/cloud/alloydb/connector/connector.py
+++ b/google/cloud/alloydb/connector/connector.py
@@ -206,8 +206,14 @@ async def connect_async(self, instance_uri: str, driver: str, **kwargs: Any) ->
         # if ip_type is str, convert to IPTypes enum
         if isinstance(ip_type, str):
             ip_type = IPTypes(ip_type.upper())
-        conn_info = await cache.connect_info()
-        ip_address = conn_info.get_preferred_ip(ip_type)
+        try:
+            conn_info = await cache.connect_info()
+            ip_address = conn_info.get_preferred_ip(ip_type)
+        except Exception:
+            # with an error from AlloyDB API call or IP type, invalidate the
+            # cache and re-raise the error
+            await self._remove_cached(instance_uri)
+            raise
         logger.debug(f"['{instance_uri}']: Connecting to {ip_address}:5433")
 
         # synchronous drivers are blocking and run using executor
@@ -334,6 +340,15 @@ def metadata_exchange(
 
         return sock
 
+    async def _remove_cached(self, instance_uri: str) -> None:
+        """Stops all background refreshes and deletes the connection
+        info cache from the map of caches.
+        """
+        logger.debug(f"['{instance_uri}']: Removing connection info from cache")
+        # remove cache from stored caches and close it
+        cache = self._cache.pop(instance_uri)
+        await cache.close()
+
     def __enter__(self) -> "Connector":
         """Enter context manager by returning Connector object"""
         return self
diff --git a/google/cloud/alloydb/connector/version.py b/google/cloud/alloydb/connector/version.py
index f6d5c1cd..06fadc0e 100644
--- a/google/cloud/alloydb/connector/version.py
+++ b/google/cloud/alloydb/connector/version.py
@@ -12,4 +12,4 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-__version__ = "1.5.0"
+__version__ = "1.6.0"
diff --git a/requirements-test.txt b/requirements-test.txt
index 11bf97eb..d0c14928 100644
--- a/requirements-test.txt
+++ b/requirements-test.txt
@@ -1,8 +1,9 @@
 asyncpg==0.30.0
 mock==5.1.0
 pg8000==1.31.2
-pytest==8.3.3
+pytest==8.3.4
 pytest-asyncio==0.24.0
 pytest-cov==6.0.0
 pytest-aiohttp==1.0.5
 SQLAlchemy[asyncio]==2.0.36
+aioresponses==0.7.7
diff --git a/requirements.txt b/requirements.txt
index 148b1b4f..2d898668 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,6 +1,6 @@
 aiofiles==24.1.0
-aiohttp==3.10.10
-cryptography==43.0.3
+aiohttp==3.11.10
+cryptography==44.0.0
 google-auth==2.36.0
 requests==2.32.3
 protobuf==4.25.5
diff --git a/tests/unit/test_async_connector.py b/tests/unit/test_async_connector.py
index e2b22b10..0f150875 100644
--- a/tests/unit/test_async_connector.py
+++ b/tests/unit/test_async_connector.py
@@ -15,6 +15,7 @@
 import asyncio
 from typing import Union
 
+from aiohttp import ClientResponseError
 from mock import patch
 from mocks import FakeAlloyDBClient
 from mocks import FakeConnectionInfo
@@ -23,6 +24,8 @@
 
 from google.cloud.alloydb.connector import AsyncConnector
 from google.cloud.alloydb.connector import IPTypes
+from google.cloud.alloydb.connector.exceptions import IPTypeNotFoundError
+from google.cloud.alloydb.connector.instance import RefreshAheadCache
 
 ALLOYDB_API_ENDPOINT = "https://alloydb.googleapis.com"
 
@@ -294,3 +297,39 @@ async def test_async_connect_bad_ip_type(
             exc_info.value.args[0]
             == f"Incorrect value for ip_type, got '{bad_ip_type}'. Want one of: 'PUBLIC', 'PRIVATE', 'PSC'."
         )
+
+
+async def test_Connector_remove_cached_bad_instance(
+    credentials: FakeCredentials,
+) -> None:
+    """When a Connector attempts to retrieve connection info for a
+    non-existent instance, it should delete the instance from
+    the cache and ensure no background refresh happens (which would be
+    wasted cycles).
+    """
+    instance_uri = "projects/test-project/locations/test-region/clusters/test-cluster/instances/bad-test-instance"
+    async with AsyncConnector(credentials=credentials) as connector:
+        with pytest.raises(ClientResponseError):
+            await connector.connect(instance_uri, "asyncpg")
+        assert instance_uri not in connector._cache
+
+
+async def test_Connector_remove_cached_no_ip_type(credentials: FakeCredentials) -> None:
+    """When a Connector attempts to connect and preferred IP type is not present,
+    it should delete the instance from the cache and ensure no background refresh
+    happens (which would be wasted cycles).
+    """
+    instance_uri = "projects/test-project/locations/test-region/clusters/test-cluster/instances/test-instance"
+    # set instance to only have Public IP
+    fake_client = FakeAlloyDBClient()
+    fake_client.instance.ip_addrs = {"PUBLIC": "127.0.0.1"}
+    async with AsyncConnector(credentials=credentials) as connector:
+        connector._client = fake_client
+        # populate cache
+        cache = RefreshAheadCache(instance_uri, fake_client, connector._keys)
+        connector._cache[instance_uri] = cache
+        # test instance does not have Private IP, thus should invalidate cache
+        with pytest.raises(IPTypeNotFoundError):
+            await connector.connect(instance_uri, "asyncpg", ip_type="private")
+        # check that cache has been removed from dict
+        assert instance_uri not in connector._cache
diff --git a/tests/unit/test_client.py b/tests/unit/test_client.py
index 3da68079..e4b2fdbb 100644
--- a/tests/unit/test_client.py
+++ b/tests/unit/test_client.py
@@ -15,7 +15,9 @@
 import json
 from typing import Any, Optional
 
+from aiohttp import ClientResponseError
 from aiohttp import web
+from aioresponses import aioresponses
 from mocks import FakeCredentials
 import pytest
 
@@ -138,6 +140,75 @@ async def test__get_metadata_with_psc(
     }
 
 
+async def test__get_metadata_error(
+    credentials: FakeCredentials,
+) -> None:
+    """
+    Test that AlloyDB API error messages are raised for _get_metadata.
+    """
+    # mock AlloyDB API calls with exceptions
+    client = AlloyDBClient(
+        alloydb_api_endpoint="https://alloydb.googleapis.com",
+        quota_project=None,
+        credentials=credentials,
+    )
+    get_url = "https://alloydb.googleapis.com/v1beta/projects/my-project/locations/my-region/clusters/my-cluster/instances/my-instance/connectionInfo"
+    resp_body = {
+        "error": {
+            "code": 403,
+            "message": "AlloyDB API has not been used in project 123456789 before or it is disabled",
+        }
+    }
+    with aioresponses() as mocked:
+        mocked.get(
+            get_url,
+            status=403,
+            payload=resp_body,
+            repeat=True,
+        )
+        with pytest.raises(ClientResponseError) as exc_info:
+            await client._get_metadata(
+                "my-project", "my-region", "my-cluster", "my-instance"
+            )
+        assert exc_info.value.status == 403
+        assert (
+            exc_info.value.message
+            == "AlloyDB API has not been used in project 123456789 before or it is disabled"
+        )
+    await client.close()
+
+
+async def test__get_metadata_error_parsing_json(
+    credentials: FakeCredentials,
+) -> None:
+    """
+    Test that aiohttp default error messages are raised when _get_metadata gets
+    a bad JSON response.
+    """
+    # mock AlloyDB API calls with exceptions
+    client = AlloyDBClient(
+        alloydb_api_endpoint="https://alloydb.googleapis.com",
+        quota_project=None,
+        credentials=credentials,
+    )
+    get_url = "https://alloydb.googleapis.com/v1beta/projects/my-project/locations/my-region/clusters/my-cluster/instances/my-instance/connectionInfo"
+    resp_body = ["error"]  # invalid json
+    with aioresponses() as mocked:
+        mocked.get(
+            get_url,
+            status=403,
+            payload=resp_body,
+            repeat=True,
+        )
+        with pytest.raises(ClientResponseError) as exc_info:
+            await client._get_metadata(
+                "my-project", "my-region", "my-cluster", "my-instance"
+            )
+        assert exc_info.value.status == 403
+        assert exc_info.value.message == "Forbidden"
+    await client.close()
+
+
 @pytest.mark.asyncio
 async def test__get_client_certificate(
     client: Any, credentials: FakeCredentials
@@ -157,6 +228,72 @@ async def test__get_client_certificate(
     assert cert_chain[2] == "This is the root cert"
 
 
+async def test__get_client_certificate_error(
+    credentials: FakeCredentials,
+) -> None:
+    """
+    Test that AlloyDB API error messages are raised for _get_client_certificate.
+    """
+    # mock AlloyDB API calls with exceptions
+    client = AlloyDBClient(
+        alloydb_api_endpoint="https://alloydb.googleapis.com",
+        quota_project=None,
+        credentials=credentials,
+    )
+    post_url = "https://alloydb.googleapis.com/v1beta/projects/my-project/locations/my-region/clusters/my-cluster:generateClientCertificate"
+    resp_body = {
+        "error": {
+            "code": 404,
+            "message": "The AlloyDB instance does not exist.",
+        }
+    }
+    with aioresponses() as mocked:
+        mocked.post(
+            post_url,
+            status=404,
+            payload=resp_body,
+            repeat=True,
+        )
+        with pytest.raises(ClientResponseError) as exc_info:
+            await client._get_client_certificate(
+                "my-project", "my-region", "my-cluster", ""
+            )
+        assert exc_info.value.status == 404
+        assert exc_info.value.message == "The AlloyDB instance does not exist."
+    await client.close()
+
+
+async def test__get_client_certificate_error_parsing_json(
+    credentials: FakeCredentials,
+) -> None:
+    """
+    Test that aiohttp default error messages are raised when
+    _get_client_certificate gets a bad JSON response.
+    """
+    # mock AlloyDB API calls with exceptions
+    client = AlloyDBClient(
+        alloydb_api_endpoint="https://alloydb.googleapis.com",
+        quota_project=None,
+        credentials=credentials,
+    )
+    post_url = "https://alloydb.googleapis.com/v1beta/projects/my-project/locations/my-region/clusters/my-cluster:generateClientCertificate"
+    resp_body = ["error"]  # invalid json
+    with aioresponses() as mocked:
+        mocked.post(
+            post_url,
+            status=404,
+            payload=resp_body,
+            repeat=True,
+        )
+        with pytest.raises(ClientResponseError) as exc_info:
+            await client._get_client_certificate(
+                "my-project", "my-region", "my-cluster", ""
+            )
+        assert exc_info.value.status == 404
+        assert exc_info.value.message == "Not Found"
+    await client.close()
+
+
 @pytest.mark.asyncio
 async def test_AlloyDBClient_init_(credentials: FakeCredentials) -> None:
     """
diff --git a/tests/unit/test_connector.py b/tests/unit/test_connector.py
index 95b62239..a02ad30e 100644
--- a/tests/unit/test_connector.py
+++ b/tests/unit/test_connector.py
@@ -16,6 +16,7 @@
 from threading import Thread
 from typing import Union
 
+from aiohttp import ClientResponseError
 from mock import patch
 from mocks import FakeAlloyDBClient
 from mocks import FakeCredentials
@@ -23,6 +24,9 @@
 
 from google.cloud.alloydb.connector import Connector
 from google.cloud.alloydb.connector import IPTypes
+from google.cloud.alloydb.connector.exceptions import IPTypeNotFoundError
+from google.cloud.alloydb.connector.instance import RefreshAheadCache
+from google.cloud.alloydb.connector.utils import generate_keys
 
 
 def test_Connector_init(credentials: FakeCredentials) -> None:
@@ -203,3 +207,44 @@ def test_Connector_close_called_multiple_times(credentials: FakeCredentials) ->
     assert connector._thread.is_alive() is False
     # call connector.close a second time
     connector.close()
+
+
+def test_Connector_remove_cached_bad_instance(
+    credentials: FakeCredentials,
+) -> None:
+    """When a Connector attempts to retrieve connection info for a
+    non-existent instance, it should delete the instance from
+    the cache and ensure no background refresh happens (which would be
+    wasted cycles).
+    """
+    instance_uri = "projects/test-project/locations/test-region/clusters/test-cluster/instances/bad-test-instance"
+    with Connector(credentials) as connector:
+        with pytest.raises(ClientResponseError):
+            connector.connect(instance_uri, "pg8000")
+        assert instance_uri not in connector._cache
+
+
+async def test_Connector_remove_cached_no_ip_type(credentials: FakeCredentials) -> None:
+    """When a Connector attempts to connect and preferred IP type is not present,
+    it should delete the instance from the cache and ensure no background refresh
+    happens (which would be wasted cycles).
+    """
+    instance_uri = "projects/test-project/locations/test-region/clusters/test-cluster/instances/test-instance"
+    # set instance to only have Public IP
+    fake_client = FakeAlloyDBClient()
+    fake_client.instance.ip_addrs = {"PUBLIC": "127.0.0.1"}
+    with Connector(credentials=credentials) as connector:
+        connector._client = fake_client
+        connector._keys = asyncio.wrap_future(
+            asyncio.run_coroutine_threadsafe(
+                generate_keys(), asyncio.get_running_loop()
+            ),
+            loop=asyncio.get_running_loop(),
+        )
+        cache = RefreshAheadCache(instance_uri, fake_client, connector._keys)
+        connector._cache[instance_uri] = cache
+        # test instance does not have Private IP, thus should invalidate cache
+        with pytest.raises(IPTypeNotFoundError):
+            await connector.connect_async(instance_uri, "pg8000", ip_type="private")
+        # check that cache has been removed from dict
+        assert instance_uri not in connector._cache