Engine coolant temperature sensor output stuck at high engine coolant temperature:
WARNING: This page is about a different car, the 2004 Lexus ES 330. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Engine Coolant Temperature Sensor Output Stuck At High Engine Coolant Temperature Typical Enabling Conditions Table
*1 Vehicle is stopped for 20 seconds or more and accelerated to more than 44 mph (70 km/h) within 40 seconds.
*2 Vehicle is driven by 40 mph (65 km/h) or more for 30 seconds or more and the vehicle speed reaches 44 mph (70 km/h). The vehicle is decelerated from 40 mph (65 km/h) to 2 mph (3 km/h) or less within 35 seconds and stopped for 10 seconds.