diff --git a/AGENTS.md b/AGENTS.md
index 225ae49..24faf39 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -132,6 +132,7 @@ Source protobuf definitions live in `proto/`; generated Python files live in `te
 - **`expects_data` splits BLE reply-waiting: VCSEC actuations return on the terminal ack**: a VCSEC read replies with a bare ACK **then** a data frame, but a VCSEC actuation (RKE/closure/wake via `_sendVehicleSecurity`) replies with a **single bare ACK only** - `_send` cannot tell the two apart at transport level, so the caller declares it. `_sendVehicleSecurity` passes `expects_data=False` down through `_command` into `_send` (`commands.py`/`bluetooth.py`); everything else (VCSEC reads via `_getVehicleSecurity`, all infotainment via `_send/_getInfotainment`, `_handshake`, `pair`) keeps the default `expects_data=True`. With `expects_data=False`, `_send` returns immediately on the matching ACK instead of waiting out `_ack_followup_timeout` (was a flat ~2s tax on every VCSEC actuation), and on a lost ack it raises `BluetoothTimeout` after the shorter `_actuation_timeout` (2s) rather than `_default_timeout` (5s) - the verify-by-state contract makes a longer wait pointless. Infotainment actuations never paid the tax (their `actionStatus` rides in `protobuf_message_as_bytes`, so `_send` returns on that data frame). The WAIT/fault retry threads `expects_data` through unchanged, so the double-execute exposure noted above is unaffected.
 - **`navigation_gps_request`'s `order` param is a raw int, not a callable enum**: `commands.py` used to build it as `NavigationGpsRequest.RemoteNavTripOrder(order)`, treating the protobuf nested-enum wrapper (`EnumTypeWrapper`) as if it were a callable Python `enum.IntEnum` class - it isn't, so every call raised `TypeError` before any message was sent (found live during PR-8; this method had never been exercised over BLE before). Fixed to pass `order=order` directly (matching the working sibling `navigation_gps_destination_request`), which protobuf accepts as a bare int for an enum field at runtime.
 - **`ReassemblingBuffer` resets on a >1s inter-chunk gap, not just on decode failure**: `bluetooth.py`'s `ReassemblingBuffer.receive_data` discards any in-progress partial frame if the next chunk arrives more than `STALE_CHUNK_TIMEOUT` (1s) after the previous one, mirroring Tesla's official Go SDK (`teslamotors/vehicle-command`, `pkg/connector/ble/ble.go`'s `rxTimeout`). Without this, a chunk dropped mid-message left a stale partial in the buffer that got prepended to the next message, corrupting it until a lucky decode failure resynced. This is a frame-integrity hardening, not a fix for the separate ack-loss behavior documented above (that's a stalled/silent link, which no buffer-side reset can recover).
+- **Cross-transport parity (cloud REST `VehicleFleet` vs BLE `Commands`)**: the same-named command on both paths should build a semantically equivalent instruction from identical args - a divergence there is a bug, but response *bodies* legitimately differ (REST JSON dict vs decoded protobuf) and are not. `tests/test_cross_transport_parity.py` locks the equivalence in with mocked-both-transports tests. Known **non-bug FORM differences** (do not "fix"): `set_scheduled_departure`'s `preconditioning_enabled`/`off_peak_charging_enabled` (no proto fields), `window_control` lat/lon and `navigation_sc_request` `id` (no proto fields), `navigation_request`'s `type`/`locale`/`timestamp_ms` (REST share-intent framing), and `media_volume_up` (no Tesla REST endpoint - BLE-only; cloud raises volume via `adjust_volume`). Two **open divergences left unfixed** pending live verification: `clear_pin_to_drive_admin` builds `DrivingClearSpeedLimitPinAction` (speed-limit PIN, not PIN-to-Drive - suspected mismapping, security-sensitive), and `navigation_gps_request`'s `order` is required on BLE but optional on cloud (signature mismatch; null-order wire semantics undecided).
 
 ## Maintaining this file
 
diff --git a/docs/bluetooth_vehicles.md b/docs/bluetooth_vehicles.md
index a953ed0..0025a2a 100644
--- a/docs/bluetooth_vehicles.md
+++ b/docs/bluetooth_vehicles.md
@@ -309,6 +309,9 @@ commands:
 - `media_next_fav()`
 - `media_prev_fav()`
 
+`adjust_volume(volume)` accepts absolute volume values from `0.0` through
+`11.0`, matching the Fleet API command validation.
+
 These commands return the signed-command acknowledgement, not a media-state
 diff. For verification, prefer `media_state().audio_volume` and
 `media_state().media_playback_status` where they apply. Track identity fields
diff --git a/docs/fleet_api_signed_commands.md b/docs/fleet_api_signed_commands.md
index 9dfa3e7..dafcc61 100644
--- a/docs/fleet_api_signed_commands.md
+++ b/docs/fleet_api_signed_commands.md
@@ -187,6 +187,9 @@ actually executed despite the WAIT/fault reply. Verify commands such as media
 toggles, volume steps, and schedule add/remove operations by reading absolute
 state after the call instead of relying on the number of send attempts.
 
+`adjust_volume(volume)` accepts absolute volume values from `0.0` through
+`11.0`, matching the Fleet API command validation.
+
 ## Flash Lights
 
 You can flash the lights of a specific vehicle using its VIN:
diff --git a/tesla_fleet_api/tesla/vehicle/commands.py b/tesla_fleet_api/tesla/vehicle/commands.py
index 94013d1..6c73080 100644
--- a/tesla_fleet_api/tesla/vehicle/commands.py
+++ b/tesla_fleet_api/tesla/vehicle/commands.py
@@ -756,7 +756,9 @@ async def actuate_trunk(self, which_trunk: Trunk | str) -> dict[str, Any]:
         raise ValueError("Invalid trunk.")
 
     async def adjust_volume(self, volume: float) -> dict[str, Any]:
-        """Adjusts vehicle media playback volume."""
+        """Adjusts vehicle media playback volume from 0.0 to 11.0."""
+        if volume < 0.0 or volume > 11.0:
+            raise ValueError("Volume must a number from 0.0 to 11.0")
         return await self._sendInfotainment(
             Action(
                 vehicleAction=VehicleAction(
diff --git a/tesla_fleet_api/tesla/vehicle/fleet.py b/tesla_fleet_api/tesla/vehicle/fleet.py
index c958697..715032c 100644
--- a/tesla_fleet_api/tesla/vehicle/fleet.py
+++ b/tesla_fleet_api/tesla/vehicle/fleet.py
@@ -42,7 +42,7 @@ async def actuate_trunk(self, which_trunk: Trunk | str) -> dict[str, Any]:
         )
 
     async def adjust_volume(self, volume: float) -> dict[str, Any]:
-        """Adjusts vehicle media playback volume."""
+        """Adjusts vehicle media playback volume from 0.0 to 11.0."""
         if volume < 0.0 or volume > 11.0:
             raise ValueError("Volume must a number from 0.0 to 11.0")
         return await self._request(
@@ -582,7 +582,8 @@ async def trigger_homelink(
         data: dict[str, str | float] = {}
         if token:
             data["token"] = token
-        if lat and lon:
+        # Guard on None, not truthiness: lat/lon of 0.0 are valid coordinates.
+        if lat is not None and lon is not None:
             data["lat"] = lat
             data["lon"] = lon
         return await self._request(
diff --git a/tests/test_cross_transport_parity.py b/tests/test_cross_transport_parity.py
new file mode 100644
index 0000000..02a6f74
--- /dev/null
+++ b/tests/test_cross_transport_parity.py
@@ -0,0 +1,124 @@
+"""Cross-transport parity: the same Python call must build semantically
+equivalent vehicle instructions over the Fleet REST (cloud) path and the BLE
+signed-command (protobuf) path.
+
+Response bodies legitimately differ in FORM (cloud returns a REST JSON dict,
+BLE returns decoded protobuf), so these tests assert on the *outbound
+instruction* each transport constructs from identical arguments - that is where
+a parameter-handling divergence between the two code paths would show up.
+
+The cloud path is exercised through ``VehicleFleet`` with ``_request`` mocked;
+the BLE path through ``VehicleBluetooth`` with ``_send`` mocked (see
+``ble_mocked_transport``).
+"""
+
+from __future__ import annotations
+
+from typing import Any, cast
+from unittest.mock import AsyncMock, MagicMock
+
+from tesla_fleet_api.tesla.vehicle.bluetooth import VehicleBluetooth
+from tesla_fleet_api.tesla.vehicle.fleet import VehicleFleet
+from tesla_fleet_api.tesla.vehicle.proto.car_server_pb2 import Action, VehicleAction
+from tesla_fleet_api.tesla.vehicle.proto.universal_message_pb2 import RoutableMessage
+
+from ble_mocked_transport import (
+    MockedBleTransportTestCase,
+    decrypt_sent_command,
+    infotainment_action_ok_reply,
+)
+
+
+def _make_fleet_vehicle(vin: str) -> tuple[VehicleFleet[Any], AsyncMock]:
+    """A ``VehicleFleet`` whose ``_request`` is mocked to capture the REST call."""
+    parent = MagicMock()
+    request = AsyncMock(return_value={"response": {"result": True}})
+    parent._request = request  # pyright: ignore[reportAttributeAccessIssue]
+    return VehicleFleet(parent, vin), request
+
+
+def _sent_vehicle_action(
+    vehicle: VehicleBluetooth[Any], send: AsyncMock
+) -> VehicleAction:
+    """Decrypt the signed command the BLE transport was about to send."""
+    assert send.await_args is not None
+    sent_msg = cast("RoutableMessage", send.await_args.args[0])
+    plaintext = decrypt_sent_command(vehicle, sent_msg)
+    return Action.FromString(plaintext).vehicleAction
+
+
+class TriggerHomelinkParityTests(MockedBleTransportTestCase):
+    """``trigger_homelink`` must carry the given coordinates on both transports.
+
+    Regression: the cloud path used a truthy ``if lat and lon`` check that
+    silently dropped a valid ``0.0`` coordinate, while BLE (``is not None``)
+    kept it - a genuine parameter-handling divergence.
+    """
+
+    async def test_zero_coordinates_survive_on_both_transports(self) -> None:
+        # Cloud (REST)
+        cloud, request = _make_fleet_vehicle(self.VIN)
+        await cloud.trigger_homelink(token="tok", lat=0.0, lon=0.0)
+        assert request.await_args is not None
+        cloud_json = request.await_args.kwargs["json"]
+        self.assertEqual(cloud_json["lat"], 0.0)
+        self.assertEqual(cloud_json["lon"], 0.0)
+        self.assertEqual(cloud_json["token"], "tok")
+
+        # BLE (signed protobuf)
+        ble, send = self.make_vehicle()
+        send.return_value = infotainment_action_ok_reply()
+        await ble.trigger_homelink(token="tok", lat=0.0, lon=0.0)
+        action = _sent_vehicle_action(ble, send).vehicleControlTriggerHomelinkAction
+        self.assertEqual(action.location.latitude, 0.0)
+        self.assertEqual(action.location.longitude, 0.0)
+        self.assertEqual(action.token, "tok")
+
+    async def test_omitted_coordinates_absent_on_both_transports(self) -> None:
+        cloud, request = _make_fleet_vehicle(self.VIN)
+        await cloud.trigger_homelink(token="tok")
+        assert request.await_args is not None
+        cloud_json = request.await_args.kwargs["json"]
+        self.assertNotIn("lat", cloud_json)
+        self.assertNotIn("lon", cloud_json)
+
+        ble, send = self.make_vehicle()
+        send.return_value = infotainment_action_ok_reply()
+        await ble.trigger_homelink(token="tok")
+        action = _sent_vehicle_action(ble, send).vehicleControlTriggerHomelinkAction
+        # No location submessage set when coordinates are omitted.
+        self.assertFalse(action.HasField("location"))
+
+
+class AdjustVolumeParityTests(MockedBleTransportTestCase):
+    """``adjust_volume`` must reject the same out-of-range values on both
+    transports.
+
+    Regression: the cloud path validated ``0.0 <= volume <= 11.0`` and raised
+    ``ValueError``; the BLE path forwarded any float to the car unchecked - a
+    parameter-validation divergence.
+    """
+
+    async def test_out_of_range_rejected_on_both_transports(self) -> None:
+        for bad in (-1.0, 11.5):
+            cloud, request = _make_fleet_vehicle(self.VIN)
+            with self.assertRaises(ValueError):
+                await cloud.adjust_volume(bad)
+            request.assert_not_awaited()
+
+            ble, send = self.make_vehicle()
+            with self.assertRaises(ValueError):
+                await ble.adjust_volume(bad)
+            send.assert_not_awaited()
+
+    async def test_in_range_sends_absolute_volume_on_both_transports(self) -> None:
+        cloud, request = _make_fleet_vehicle(self.VIN)
+        await cloud.adjust_volume(5.0)
+        assert request.await_args is not None
+        self.assertEqual(request.await_args.kwargs["json"], {"volume": 5.0})
+
+        ble, send = self.make_vehicle()
+        send.return_value = infotainment_action_ok_reply()
+        await ble.adjust_volume(5.0)
+        action = _sent_vehicle_action(ble, send)
+        self.assertAlmostEqual(action.mediaUpdateVolume.volume_absolute_float, 5.0)