Parts for your 2011 Subaru Forester-Temperature sensors

2011 Subaru Forester temperature sensors — what they do and how to look after them

Temperature sensors absolutely are used on the 2011 Subaru Forester (SH series). Factory documentation—Subaru Service Manual (Engine Control, Cooling, HVAC and Transmission sections for MY2011 Forester SH), Subaru New Model/Technical Training for SH Forester, and the OBD-II diagnostics listed by Subaru for DTCs P0110–P0114, P0115–P0119 and P0710–P0713—identify multiple temperature sensors fitted from the factory. These include the engine coolant temperature sensor (ECT), the intake air temperature sensor (IAT), the ambient/outside air temperature sensor for HVAC/cluster, and an automatic transmission fluid (ATF) temperature sensor on 4EAT models.

On this Forester, temperature sensors are the quiet achievers that keep things running sweet. The ECT tells the ECU how warm the engine is so it can sort cold starts, fuel trim, ignition timing and fan control. The IAT helps tweak fuelling and spark based on charge air density. The ambient temp sensor supports HVAC performance and the outside-temp display, while the ATF sensor protects the auto by adjusting shift strategy and setting failsafes if the fluid runs hot.

• Engine Coolant Temperature (ECT): NTC thermistor in the coolant passage, drives fans and engine strategy.
• Intake Air Temperature (IAT): On non‑turbo EJ25 it’s integrated in the MAF housing, on turbo models it’s located in the charge/intake tract.
• Ambient Air Temperature: Sits ahead of the radiator support, feeds HVAC and the dash display.
• ATF Temperature (4EAT only): Inside the transmission, used by the TCM for shift and protection logic.

There’s no fixed replacement interval in Subaru’s schedule, they’re service‑on‑condition parts. Still, it pays to check them during regular servicing, especially if there are symptoms like hard cold starts, erratic idle, rich running, the radiator fans stuck on or off, poor A/C performance, an AT temp light, or fault codes such as P0115–P0119 (ECT), P0110–P0114 (IAT) or P0710–P0713 (ATF temp).

• Scan live data under the bonnet: compare ECT/IAT readings to actual ambient when cold, they should match within a few degrees.
• Inspect connectors and earths for corrosion or broken clips—very common causes of flaky readings.
• Keep coolant fresh and correct (Subaru‑spec premix), sludge and air pockets can mislead the ECT and cause fan issues.
• If replacing, use an OEM‑spec sensor and a new sealing washer where required, and torque to the Subaru Service Manual spec. Work on a cold engine, expect a small coolant loss on ECT swaps, then top up and bleed properly.
• On non‑turbo models, a dirty MAF can skew IAT—clean with MAF‑safe cleaner, never with anything abrasive.

Technical sources: Subaru Forester (SH) MY2011 Factory Service Manual (Engine, Cooling, HVAC and AT sections), Subaru Technical Training/New Model Features (SH Forester), and Subaru’s OBD‑II DTC listings covering P0110–P0114, P0115–P0119 and P0710–P0713 for this platform.

Where is the engine coolant temperature sensor on a 2011 Forester?
It’s mounted on the coolant cross‑over pipe beneath the intake manifold, toward the front/top of the EJ25 engine. Access is from above under the bonnet, remove intake ducting for room. Always start with a cold engine to avoid burns and coolant spray.

Do you have to drain the coolant to replace the ECT sensor?
Not fully. You’ll lose a small amount when the sensor is removed. Plug the hole quickly, fit the new sensor and washer, then top up with the correct Subaru‑spec coolant and bleed the system. A no‑spill funnel helps, and the heater should be set to hot during bleeding.

Can a dodgy temp sensor make the radiator fans run all the time?
Yes. If the ECT reports an implausibly high temperature, the ECU may command the fans on as a safety measure. Confirm with a scan tool, check wiring/connectors, and only then replace the sensor if the readings are out of whack.