diff --git a/deploy/yaris-obd.service b/deploy/yaris-obd.service
index d608685..7cbf669 100644
--- a/deploy/yaris-obd.service
+++ b/deploy/yaris-obd.service
@@ -12,6 +12,11 @@ WorkingDirectory=/home/yaris/app/yaris-obd
 # the log file promptly instead of sitting in Python's stdout buffer indefinitely
 # when it's redirected to a file instead of a TTY.
 Environment=PYTHONUNBUFFERED=1
+# Once OBD is confirmed working on this car, pin the protocol to skip the
+# 3-5s auto-detect probe on every ignition-on: e.g. OBD_PROTOCOL=6 for
+# ISO 15765-4 CAN 11-bit 500kbps (correct for 2013 Toyota Yaris).
+# Leave unset during initial setup so auto-detect can find the right value.
+#Environment=OBD_PROTOCOL=6
 ExecStart=/home/yaris/app/yaris-obd/venv/bin/python app.py
 Restart=on-failure
 RestartSec=5
diff --git a/modules/app_obd.py b/modules/app_obd.py
index c564b42..805c57e 100644
--- a/modules/app_obd.py
+++ b/modules/app_obd.py
@@ -52,10 +52,13 @@ connection = None
 
 
 def _decode_odometer(messages):
-    data = messages[0].data[2:]
-    if len(data) != 4:
-        raise ValueError(f"expected 4 odometer bytes, received {len(data)}")
-    return int.from_bytes(bytes(data), byteorder="big") / 10
+    try:
+        data = messages[0].data[2:]
+        if len(data) != 4:
+            return None
+        return int.from_bytes(bytes(data), byteorder="big") / 10
+    except Exception:
+        return None
 
 
 ODOMETER_COMMAND = obd.OBDCommand(
@@ -225,6 +228,21 @@ def connect_obd():
             _emit_disconnected()
             return None
 
+        # Reset stale sensor values from the previous ignition cycle so the
+        # UI doesn't briefly display outdated readings before the first polls.
+        global rpm, coolant_temp, fuel_level, throttle_position, mil_on, dtc_codes, odometer
+        global mil_updated_at, dtc_updated_at, speed_updated_at
+        rpm = None
+        coolant_temp = None
+        fuel_level = None
+        throttle_position = None
+        mil_on = None
+        dtc_codes = []
+        odometer = None
+        mil_updated_at = None
+        dtc_updated_at = None
+        speed_updated_at = None
+
         _log_connection_diagnostics(candidate)
         app_events.socketio.emit("obd_status", obd_status[1])
         _start_polling_threads()