Parts for your 2012 Subaru Forester-Temperature sensors

2012 Subaru Forester temperature sensors: what they do and when to service them

Temperature sensors absolutely are fitted to the 2012 Subaru Forester and they’re central to how the car runs. The Factory Service Manual for the 2012 Forester (Subaru TechInfo, Engine Control System and Diagnostics sections) details multiple temperature inputs used by the ECU/TCM and HVAC systems, including the engine coolant temperature (ECT) sensor, intake air temperature (IAT) sensing (integrated with the MAF on the FB25), ambient/outside air temperature for the A/C and dash display, the A/T fluid temperature sensor on 4EAT models, and HVAC evaporator thermistors. Subaru’s wiring diagrams and parts catalog for MY12 Forester also show these sensors and their circuits as standard equipment.

On the FB25-powered 2012 Forester, the ECT sensor tells the engine computer how hot the coolant is, shaping cold-start enrichment, idle speed, ignition timing, radiator fan operation and over-temp protection. The IAT input helps the ECU adjust fueling for air density. The ambient temp sensor feeds the climate control and the instrument cluster’s outside temp readout. If it’s a 4-speed auto (4EAT), the transmission control uses the ATF temperature sensor to manage shift strategy and protect the gearbox when fluid is too hot or too cold. All of this is straight out of the Subaru service manual and wiring book for the model year.

There’s no set replacement interval for these sensors, but they should be checked whenever drivability issues or cooling-system faults pop up. A healthy cooling system keeps the ECT sensor honest, so fresh, correct Subaru-spec coolant, a sound thermostat, and no air locks under the bonnet are key. If scan data shows implausible ECT/IAT readings, the fans run constantly, the gauge behaves oddly, or there are codes like P0117/P0118 (ECT) or IAT circuit faults, inspect connectors for corrosion, check harness integrity, and replace the sensor if it’s out of spec. On cars with the 4EAT, ATF temperature codes (e.g., P0711/P0713) warrant checking fluid condition and the transmission harness before condemning the sensor.

• Use an OBD-II scan tool to compare live ECT to an infrared reading at the thermostat housing when cold and at operating temp.
• If the IAT is built into the MAF, clean the MAF element only with proper MAF cleaner, don’t touch the element.
• When replacing an ECT sensor, follow factory torque and sealing guidance from the service manual and bleed the cooling system properly.
• Use quality OEM or reputable aftermarket sensors to avoid flaky readings.

Technical references: 2012 Subaru Forester Factory Service Manual (Engine Control System, Diagnostics, and HVAC sections), Subaru Wiring Diagram Book (MY12 Forester), and Subaru Genuine Parts Catalog listings for temperature sensors.

Popular questions

Where is the engine coolant temperature sensor on a 2012 Forester?
It’s mounted on the engine coolant passage on the FB25, near the thermostat/water outlet area. Access is from the top under the bonnet, remove intake ducting as needed. The exact spot and connector pinout are shown in the 2012 Forester service manual and wiring diagram.

What are the signs a temperature sensor has failed?
Hard cold starts, high idle when warm, radiator fans running all the time, erratic temp gauge or outside temp reading, poor fuel economy, and check engine light with ECT/IAT or ATF temp codes. Live scan data that doesn’t track actual temperature is a giveaway.

Does the 2012 Forester have an ambient temperature sensor for the A/C?
Yes. There’s an outside air temp sensor at the front of the car (near the grille/radiator support) that feeds the climate control and dash display. If it reports incorrectly, A/C performance and the displayed outside temperature can be off.