Parts for your 2015 Subaru Forester-Temperature sensors

2015 Subaru Forester temperature sensors — purpose, care, and when to swap them

Temperature sensors are absolutely used on the 2015 Subaru Forester. Technical references including the Subaru Factory Service Manual for 2015MY Forester (Engine Diagnostics, Fuel Injection, HVAC, and CVT Control sections) and Subaru New Car Features documentation confirm multiple temperature sensors: engine coolant temperature (ECT), intake air temperature (IAT), ambient air temperature for the climate control, and transmission fluid temperature for the Lineartronic CVT. These sensors are core to engine management, cooling, emissions, and drivability.

On a 2015 Forester, the ECT sensor feeds the ECU so it can set cold-start fuel, ignition timing, radiator fan operation, and thermostat strategies. The IAT sensor (integrated with the MAF on FB25 models, manifold-mounted on FA20DIT turbo) helps adjust fuelling for air density changes. The ambient temp sensor drives the A/C logic and the dash temperature read-out, and the CVT’s internal ATF temperature sensor protects the transmission from heat, adjusting line pressure and shift strategy when things get toasty. These roles are detailed in Subaru’s 2015MY FSM: Engine (Diagnostics/Fuel Injection), HVAC Control System, and CVT Control System sections.

As part of servicing a 2015 Forester, a shop should:

• Scan for DTCs and live data (ECT, IAT, ambient, CVT temp) to confirm sensors match reality, especially after cooling system or intake work.
• Check cooling system health (coolant age, leaks, radiator performance, thermostat operation), an ECT that reads hot often flags a cooling issue, not just a dud sensor.
• Inspect connectors and looms for corrosion or chafing near the thermostat housing, airbox/MAF, front bumper (ambient sensor), and CVT harness plugs.
• Verify fan cut-in temps via scan tool, compare to FSM specs. If readings are implausible, test sensor resistance per FSM charts.

Replacement is straightforward for most external sensors: depressurise and cool the system, swap the ECT with a new sealing washer, and bleed the cooling system properly. The IAT on FB25 is part of the MAF—if it’s out of spec, the MAF assembly is typically replaced. The ambient sensor lives behind the grille and is a quick swap if it’s been knocked or water-damaged. The CVT fluid temperature sensor is internal, faults here usually call for diagnostic confirmation and, if needed, valve body or internal repair rather than a simple driveway replacement.

Technical sources: Subaru 2015MY Forester Factory Service Manual (Engine Diagnostics, Fuel Injection, Cooling, HVAC Control, and CVT Control sections), Subaru New Car Features (2014–2015 Forester).

• Where is the engine coolant temperature sensor on a 2015 Forester?
  On FB25 models it’s threaded into the coolant passage near the thermostat housing at the front of the engine. Access is from the top after removing the intake snorkel. On FA20DIT (XT), it’s similarly located on the coolant crossover. A scan tool helps confirm you’ve got the right connector before you wrench it out.
• What are the signs a temperature sensor has failed?
  Hard cold starts, rich running, high idle, slow A/C engagement, erratic radiator fan behaviour, or a temp gauge that doesn’t make sense. Common fault codes include P0117/P0118 (ECT) or IAT circuit codes. Always check wiring and grounds—many “sensor” problems are actually connector or loom issues.
• Does the CVT have a temperature sensor and can it be serviced?
  Yes, the Lineartronic CVT uses an internal ATF temperature sensor for protection and shift control. It isn’t a stand-alone service item—if diagnostics confirm a fault, repair typically involves internal CVT work or valve body service. Keeping the ATF in good condition and the cooler clear helps prevent heat-related issues.