The coolant temperature sensor plug in a Subaru is connected to a sensor that gauges the engine temperature. The sensor itself is made of a metal that raises and lowers the resistance between the two terminals of the plug depending on how hot it gets. The ECU and cluster pick up this resistance value and use a base calibration to equate this input to a specific temperature. It is important to read the temperature beyond just knowing if the engine is overheating because when the car is started cold it needs a different fuel mixture compared to when the engine is hot. The correct fuel mixture means a better running car.
The quickest way to tell you may have an issue with your coolant temperature sensor plug is when the gauge isn't reading properly. Usually it is due to a bad connector since they are located on top of the engine. Being so close to the hot engine makes the plug brittle and could effect the connection.
Subaru has changed this plug multiple times over the years. It was first two separate plugs, then a three pin plug, and now it is a two pin plug. Due to changes with how Subaru communicates (Analog vs Digital) the plug has been updated. See below for more specifics about each generation. To purchase, click on one of the connectors needed below!
This plug is seen in 1998 Subaru and older. These cars use two different plugs to read the coolant temp. One is the two pin plug pictured and the second is a single pin plug that can be replaced with a spade terminal.
1998 and Older Models
This generation of plug combined the functions from the two separate plugs in the previous iteration into a single connector to send output signals to both the ECU and to the cluster.
This type of connector is used in the first generation of CANBUS equipped cars. It has an input for ground and a single output to the ECU. The ECU then sends the signal via CANBUS to the gauge cluster.
This generation uses the same input and output style as the last generation but changed the connector type.