Parts for your 2010 Subaru Legacy-Oxygen sensor

2010 Subaru Legacy oxygen sensor: what it does and when to replace it

Yes, the 2010 Subaru Legacy is fitted with oxygen-sensing hardware. Referencing the Subaru Factory Service Manual for the 2010 Legacy/Outback (Engine Diagnostics: Air/Fuel Ratio and Oxygen Sensor), Subaru parts catalogues for the EJ25, EJ255 and EZ36 engines, and OBD‑II/ADR emissions requirements applicable to 2010 passenger vehicles, this model uses a front Air/Fuel Ratio (wideband) sensor and a rear oxygen sensor. Four-cylinder variants have one of each, the 3.6R H6 has one pair per bank.

On this Legacy, the upstream Air/Fuel Ratio (A/F) sensor sits in the exhaust before the catalytic converter and constantly measures the exhaust’s oxygen content to keep the air–fuel mixture right on the money. The downstream oxygen sensor lives after the cat and keeps an eye on catalyst efficiency. Together, they help the ECU trim fuel, sharpen throttle response, keep emissions tidy, and save a few dollars at the bowser.

While Subaru doesn’t list O2 sensors as a time-based service item, they’re wear components. Heat, moisture and contaminants slowly degrade them, and it’s common to see performance taper off around 160,000–200,000 km. Telltales include a Check Engine Light, increased fuel use, a lazier idle, sulphur smells from the exhaust, and WOF/rego emissions failures. Common fault codes span P0130–P0167 for sensor circuits and P0420 for catalyst efficiency (sometimes triggered by a tired sensor rather than a bad cat).

Replacement is straightforward with the right kit. Use an OEM or OE‑equivalent sensor (typically Denso for Subaru) matched to the VIN/engine, note that the front is a wideband A/F sensor and isn’t interchangeable with the rear. A 22 mm O2 socket, penetrating oil, and patience go a long way. Many new sensors ship with thread compound, if it’s pre‑coated, don’t add extra anti‑seize. Route the loom exactly like the original, avoid twisting the leads, and tighten to the manufacturer’s torque spec. After fitting, clear codes with a scan tool and complete a drive cycle so readiness monitors set correctly.

• Upstream A/F sensor = mixture control, downstream O2 sensor = cat monitoring.
• Inspect connectors and exhaust leaks before blaming the sensor.
• If one sensor is dead at high kilometres, consider replacing the pair for consistent feedback.

How many oxygen sensors does a 2010 Subaru Legacy have?

Most 2.5‑litre four‑cylinder cars have two: one upstream A/F sensor and one downstream O2 sensor. The 3.6R H6 has four, with one A/F and one O2 sensor per bank. The 2.5GT turbo still runs a pair on its single exhaust stream.

What are the common signs or codes of a failing sensor?

Expect poorer fuel economy, rough or hunting idle, a sulphur smell, and the MIL on. Typical OBD‑II codes include P0130–P0167 for sensor/heater circuits and P0420 for catalyst efficiency. Always check for exhaust leaks and wiring issues before condemning the sensor.

Can an oxygen sensor be cleaned, or should it just be replaced?

Cleaning isn’t recommended and usually doesn’t restore accuracy. Because the sensing element is delicate and becomes contaminated internally, replacement with the correct spec sensor is the reliable fix.