Parts for your 2008 Subaru Forester-Temperature sensors

2008 Subaru Forester temperature sensors

Temperature sensors are absolutely fitted to the 2008 Subaru Forester and play key roles in engine and transmission management. This is confirmed by Subaru’s Factory Service Manual for the 2008 Forester (via Subaru Technical Information System), common OBD‑II diagnostic codes (SAE J2012) such as P0115–P0119 for the Engine Coolant Temperature (ECT) sensor and P0110–P0114 for the Intake Air Temperature (IAT) sensor, plus independent manuals like Haynes and Subaru wiring diagrams. So yes—temperature sensors matter on this model.

On the Forester’s EJ-series petrol engines, the ECT sensor feeds the ECU accurate coolant temperature so it can set cold-start enrichment, ignition timing, idle speed and radiator fan control. The IAT sensor helps the ECU trim fuel based on incoming air temperature. Auto models also rely on a transmission fluid temperature sensor for shift strategy and protection, and the climate system uses ambient and evaporator temperature sensors for cabin comfort.

• ECT: engine warm-up, mixture, timing, fan control
• IAT: mixture trimming and knock resilience
• ATF temp (auto): shift timing and protection
• Ambient/evaporator: HVAC performance

For servicing, these aren’t “change by interval” parts. Instead, check condition and data. During routine services, it’s smart to scan live data to see that coolant and intake temperatures track realistically as the engine warms. Odd readings, hard cold starts, rich running, poor fuel economy, cooling fans stuck on, an inoperative temp gauge, or DTCs (e.g., P0115, P0125, P0110) are red flags.

Coolant health directly affects the ECT sensor. Keep the cooling system in top nick: use the correct Subaru long‑life coolant, maintain the proper 50/50 mix, and replace it on schedule (typically up to 5 years/125,000 km for Subaru Super Coolant, older green formulas are often 2 years/50,000 km). Corroded connectors or earths can also skew readings—clean and protect them if needed.

When replacing an ECT sensor, work on a cold engine, relieve pressure, and catch/contain coolant. The sensor sits on the coolant crossover pipe beneath the intake manifold, just behind the alternator on most EJ engines. Swap the sealing washer or O‑ring, tighten to the factory spec (don’t overtighten), avoid thread sealant unless specified, then bleed air from the cooling system. Clear codes, verify live data and road test. For IAT faults, note that many Foresters of this era have the IAT integrated into the MAF at the airbox outlet, some variants pair it with the MAP on the manifold—replace accordingly and check for intake leaks.

Where is the engine coolant temperature (ECT) sensor on a 2008 Forester?

On most EJ engines used in 2008 Foresters, the ECT sensor is threaded into the coolant crossover pipe beneath the intake manifold, typically just behind or below the alternator. Access usually involves removing the intake snorkel and moving the alternator or related brackets for a clear path.

If in doubt, follow the upper radiator hose to the engine and trace the alloy coolant manifold—look for a two‑pin electrical connector on a small, brass‑coloured sensor body.

What are the signs a temp sensor is failing on this model?

Common clues include hard cold starts, rough idle when warm, excessive fuel use, black exhaust smoke, radiator fans running constantly, or the temp gauge behaving oddly. The check engine light may log codes like P0115–P0119 (ECT) or P0110–P0114 (IAT).

A scan tool showing unrealistic temperature readings (e.g., very low or fixed values) during warm‑up is a giveaway. Always rule out low coolant, air pockets, or corroded connectors first.

Is the IAT separate from the MAF on the 2008 Forester?

Many 2008 Foresters with a MAF sensor have the IAT built into the MAF housing at the airbox outlet. Some variants that rely more on a MAP sensor use a separate IAT in the intake manifold or ducting.

When diagnosing IAT faults, check which setup the vehicle has. If it’s integrated, replacement typically means swapping the MAF assembly. If separate, it’s a standalone, plug‑in sensor.