Parts for your 2015 Subaru Legacy-Temperature sensors

2015 Subaru Legacy temperature-sensors: what they do and how to look after them

Temperature-sensors are absolutely used on the 2015 Subaru Legacy. Factory documentation confirms several onboard temp senders that the car’s control systems rely on: the Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) sensors are detailed in the Subaru Technical Information System (2015 Legacy/Outback Service Manual, Engine Diagnostics). The HVAC section covers the Ambient Temperature Sensor for the outside temp/air-con logic, and the Lineartronic CVT manual outlines the Transmission Fluid Temperature input. These are also reflected by standard OBD-II data items defined by SAE J1979, such as PID 05 (ECT) and PID 0F (IAT). So, temperature-sensors are definitely relevant and fitted to the 2015 Legacy.

On this model, temperature-sensors help the car wake up happily on a cold morning, keep the engine in its sweet spot, and protect major components on a scorching Aussie or Kiwi summer’s day. The ECT sensor tells the engine computer how warm the coolant is so it can sort cold-start fuelling, ignition timing and radiator fan control. The IAT sensor helps fine-tune spark and fuelling as the air under the bonnet heats up. The ambient sensor informs the climate control and the dash’s outside temperature. In CVT models, transmission fluid temperature is watched closely to manage shift strategy and component protection.

They’re not regular “replace-by” items, but they do benefit from a bit of care during servicing:

• Cooling system health: fresh coolant at the correct interval, no air in the system, and no leaks. Poor coolant maintenance can give the ECT false readings.
• Clean air path: a lightly dirty MAF/IAT can skew intake temp readings, use the proper MAF-safe cleaner, not throttle body spray.
• Electrical checks: inspect connectors for corrosion, brittle clips, or rubbed-through looms, especially near the radiator support and under the intake.
• Scan tool sanity check: read live data for ECT/IAT/ATF temp. Cold engine values should sit near ambient, watch for sudden dropouts or implausible spikes.

When a sensor does fail, common signs include hard cold starts, rich running, the radiator fans staying on, erratic A/C performance, or a CVT that feels reluctant or flares. Typical fault codes include P0115–P0119 (ECT), P0112/P0113 (IAT), P0711 (ATF temp), and HVAC B14xx for the ambient thermistor. Replacement is straightforward with the right spanner and a cool engine, always follow the Subaru service manual procedure, fit a quality O-ring/seal, and refill/bleed coolant as specified. If in doubt, a quick diagnostic session can separate a flaky sensor from a wiring issue—saving time and a few dollars down the track.

• Where is the engine coolant temperature sensor on a 2015 Subaru Legacy?
  On the 2.5L FB engine it’s threaded into the coolant crossover near the thermostat housing/upper radiator hose at the front of the engine. On the 3.6R, it sits in the coolant passage on top of the block under the intake manifold. Access varies—let the engine cool completely before unplugging or removing it.
• Do temperature-sensors need regular replacement?
  Not usually. They’re monitored by the ECU and only need replacing if they fail testing or set a fault code. Routine servicing focuses on good coolant, clean air metering, and sound wiring/connectors so the sensors can do their job reliably over many kilometres.
• What symptoms point to a bad temp sensor on a Legacy?
  Think hard starts when cold, poor fuel economy, radiator fans running all the time, an erratic outside temperature reading, A/C that won’t behave, or odd CVT shift feel. A scan showing implausible ECT/IAT/ATF temperatures—or codes like P0117, P0118, P0113, or P0711—backs up the diagnosis.