Coolant thermostat:

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: Coolant Thermostat - Monitor Result (Mode 06 Data) Table

If the Test Data is less than Test Limit when the engine is warmed up, the ECM interprets this as a malfunction.

Refer to CHECKING MONITOR STATUS for detailed information on CHECKING MONITOR STATUS.