Sometimes your lucida will not change into Top Gear ive heard that it runs from a sensor in the water system is this true and does anyone know were this sensor is?

Yes, the Lucida's Top Gear function can sometimes be affected by a water temperature sensor. This sensor is usually located in the engine's cooling system, often near the thermostat or water pump. If it malfunctions or is not reading correctly, it can prevent the transmission from shifting into Top Gear. Checking the sensor and its connections can help diagnose the issue.