diff --git a/src/pyvesync/device_map.py b/src/pyvesync/device_map.py
index 172b04c3..2a0072b3 100644
--- a/src/pyvesync/device_map.py
+++ b/src/pyvesync/device_map.py
@@ -947,6 +947,8 @@ class ThermostatMap(DeviceMapTemplate):
             'LAP-V201-AUSR',
             'LAP-V201S-AUSR',
             'LAP-V201S-AEUR',
+            'LAP-P501S-WUSR',
+            'LAP-P501S-AUSR',
         ],
         modes=[
             PurifierModes.SLEEP,
diff --git a/src/pyvesync/devices/vesyncpurifier.py b/src/pyvesync/devices/vesyncpurifier.py
index ba3ba808..bf56d042 100644
--- a/src/pyvesync/devices/vesyncpurifier.py
+++ b/src/pyvesync/devices/vesyncpurifier.py
@@ -451,6 +451,17 @@ def __init__(
         """Initialize the VeSync Base API V2 Air Purifier Class."""
         super().__init__(details, manager, feature_map)
 
+    @property
+    def fan_max_level(self) -> int:
+        """Return the maximum fan speed level for this device.
+
+        The Levoit Vital Pet Pro (LAP-P501S*) has only 3 fan speeds
+        (1-3) compared to the standard Vital 200S which has 4 (1-4).
+        """
+        if 'P501S' in self.device_type:
+            return 3
+        return 4
+
     def _set_state(self, details: InnerPurifierBaseResult) -> None:
         """Set Purifier state from details response."""
         if not isinstance(details, PurifierVitalDetailsResult):
@@ -487,7 +498,7 @@ def _set_state(self, details: InnerPurifierBaseResult) -> None:
         self.state.fan_rotate_angle = details.fanRotateAngle
         if details.filterOpenState is not None:
             self.state.filter_open_state = bool(details.filterOpenState)
-        if details.timerRemain > 0:
+        if details.timerRemain is not None and details.timerRemain > 0:
             self.state.timer = Timer(details.timerRemain, 'off')
 
     @property
@@ -675,19 +686,21 @@ async def set_auto_preference(
         return True
 
     async def set_fan_speed(self, speed: None | int = None) -> bool:
+        max_level = self.fan_max_level
+        allowed_levels = list(range(1, max_level + 1))
         if speed is not None:
-            if speed not in self.fan_levels:
+            if speed not in allowed_levels:
                 _LOGGER.warning(
                     '%s is invalid speed - valid speeds are %s',
                     speed,
-                    str(self.fan_levels),
+                    str(allowed_levels),
                 )
                 return False
             new_speed = speed
         elif self.state.fan_level is None:
-            new_speed = self.fan_levels[0]
+            new_speed = allowed_levels[0]
         else:
-            new_speed = Helpers.bump_level(self.state.fan_level, self.fan_levels)
+            new_speed = Helpers.bump_level(self.state.fan_level, allowed_levels)
 
         payload_data = {'levelIdx': 0, 'manualSpeedLevel': new_speed, 'levelType': 'wind'}
         r_dict = await self.call_bypassv2_api('setLevel', payload_data)
diff --git a/src/pyvesync/models/purifier_models.py b/src/pyvesync/models/purifier_models.py
index d510ef33..80ac5cd8 100644
--- a/src/pyvesync/models/purifier_models.py
+++ b/src/pyvesync/models/purifier_models.py
@@ -38,7 +38,7 @@ class Config(BaseConfig):  # type: ignore[override]
 
 @dataclass
 class PurifierVitalDetailsResult(InnerPurifierBaseResult):
-    """Vital 100S/200S and Everest Purifier Result Model."""
+    """Vital 100S/200S, Everest, and Vital Pet Pro Purifier Result Model."""
 
     powerSwitch: int
     filterLifePercent: int
@@ -50,12 +50,12 @@ class PurifierVitalDetailsResult(InnerPurifierBaseResult):
     screenState: int
     childLockSwitch: int
     screenSwitch: int
-    lightDetectionSwitch: int
-    environmentLightState: int
-    scheduleCount: int
-    timerRemain: int
-    efficientModeTimeRemain: int
-    errorCode: int
+    scheduleCount: int | None = None
+    timerRemain: int | None = None
+    errorCode: int | None = None
+    lightDetectionSwitch: int | None = None
+    environmentLightState: int | None = None
+    efficientModeTimeRemain: int | None = None
     autoPreference: V2AutoPreferences | None = None
     fanRotateAngle: int | None = None
     filterOpenState: int | None = None
diff --git a/src/pyvesync/utils/helpers.py b/src/pyvesync/utils/helpers.py
index 89948510..0ff48a1c 100644
--- a/src/pyvesync/utils/helpers.py
+++ b/src/pyvesync/utils/helpers.py
@@ -124,6 +124,27 @@ def temperature_celsius_to_fahrenheit(celsius: float) -> float:
         return celsius * 9.0 / 5.0 + 32
 
 
+VESYNC_CERT_SHA1 = '2CA4647FA8C5C9475B13FBD47984E525F38AD3B8'
+
+
+def generate_pack_file_signature(trace_id: str) -> str:
+    """Generate the _packFileSignature header value for VeSync API requests.
+
+    The VeSync backend validates this signature using the standard AOSP test key
+    certificate SHA-1 hash rather than Etekcity's production certificate. This
+    allows us to compute the signature cleanly in Python.
+
+    Args:
+        trace_id: The traceId value from the request body.
+
+    Returns:
+        The formatted signature string, e.g. ``v0001-<sha256 hex>``.
+    """
+    raw = str(trace_id) + VESYNC_CERT_SHA1
+    h = hashlib.sha256(raw.encode('utf-8')).hexdigest()[:64].lower()
+    return f'v0001-{h}'
+
+
 class Helpers:
     """VeSync Helper Functions."""
 
diff --git a/src/pyvesync/vesync.py b/src/pyvesync/vesync.py
index 63ffc436..8adfca85 100644
--- a/src/pyvesync/vesync.py
+++ b/src/pyvesync/vesync.py
@@ -40,7 +40,10 @@
     VeSyncTokenError,
     raise_api_errors,
 )
-from pyvesync.utils.helpers import Helpers
+from pyvesync.utils.helpers import (
+    Helpers,
+    generate_pack_file_signature,
+)
 from pyvesync.utils.logs import LibraryLogger
 
 if TYPE_CHECKING:
@@ -482,6 +485,14 @@ async def async_call_api(
             req_dict = json_object
         else:
             req_dict = None
+        # Inject _packFileSignature and _signOsInfo headers when a traceId is present
+        if isinstance(req_dict, dict):
+            trace_id = req_dict.get('traceId')
+            if trace_id is None and 'payload' in req_dict:
+                trace_id = req_dict['payload'].get('traceId')
+            if headers is not None and trace_id is not None:
+                headers['_packFileSignature'] = generate_pack_file_signature(trace_id)
+                headers['_signOsInfo'] = 'Android'
         try:
             async with self.session.request(
                 method,