Coolant warning light shines blue 2010 Toyota Sienna


Very cold weather here (sub-zero). Coolant warning light shines blue and does not go off. Coolant level is topped off. Cabin heat is excellent. Bad sensor? Stuck thermostat? Thanks.much.

In this instance I would use an Infra-red temperature gun to check the temperature under the hood. You just aim at the coolant hoses, engine head and pull the trigger for an accurate reading of the actual temperature. This will let you know instantly if you actually have an overheating issue or if it is something else. Once you have confirmed it isn’t actually overheating you can concentrate on a faulty sensor or wiring issue. Test with the engine warmed up accurate readings.

toyota coolant temperature warning light

According to Kerry Toyota the right most segment of the temperature display will flash to indicate that the engine is ALMOST overheating. The warning indicates the possibility of damage and may lead to an accident. They suggest that you immediately stop the vehicle in a safe place and contact your Toyota dealer.

Coolant Sensor

You can check the resistance of the coolant temperature sensor.

2010 Toyota Siennsa coolant temperature sensor resistance specifications


  • Using an ohmmeter, measure the resistance between the terminals.
  • If the result is as specified, do not replace the engine coolant temperature sensor.
  • If the result is not as specified, replace the engine coolant temperature sensor.
In case of checking the engine coolant temperature sensor in water, do not allow water to go into the terminals. After checking, dry the engine coolant temperature sensor.