September 30: LEMON manuals is back up on a temporary server! Slowness is possible
Engine coolant temperature sensor output stuck at low 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