Parts for your 2010 Subaru Legacy-Knock sensor

2010 Subaru Legacy knock sensor — what it does and how to look after it

Based on technical sources, the 2010 Subaru Legacy is fitted with a knock sensor and it’s absolutely relevant to the car’s engine management. The Subaru Factory Service Manual for the 2010 Legacy/Outback (BM/BR) details diagnostics for knock sensor circuits (DTCs P0325, P0327, P0328), and the Subaru OEM parts catalogue lists a knock sensor for the 2.5‑litre EJ25 and EJ255 engines, and two sensors for the 3.6‑litre EZ36 H6. Industry repair databases used in workshops (e.g., Alldata/Mitchell) also provide test procedures for the knock sensor on this model year.

On this generation Legacy, the knock sensor acts like a sensitive microphone on the block. It listens for detonation (knock) and feeds that signal to the ECU, which then trims ignition timing to keep the engine safe. That means smoother running on Aussie and Kiwi petrol, better reliability on hot days or under load, and less chance of pinging up a long hill.

Engine fitment varies a touch: the 2.5 four‑cylinder usually runs a single knock sensor mounted on top of the block under the intake, while the 3.6R H6 uses a sensor on each bank. Either way, it’s a simple bolt‑down unit with a harness plug, but it’s doing a big job protecting the pistons and head.

As for servicing of your 2010 Subaru Legacy knock sensor, there’s no set replacement interval. It’s “inspect and test if needed”. During routine services, a quick visual of the sensor body and loom for cracks, heat damage or oil soaking is worthwhile, and any stored engine codes should be scanned. If diagnosed faulty, replacement is straightforward: clean the mating surface, install the new sensor in the correct orientation, and torque it to the factory spec with a torque wrench. Over‑ or under‑tightening, or twisting the connector, can make the sensor under‑ or over‑sensitive. Use quality OEM‑equivalent parts and don’t smear grease under the sensor, it needs a clean, dry contact with the block.

• Common signs of trouble: check‑engine light with P0325/P0327/P0328, noticeable pinging, rough running under load, lazy throttle response, and higher fuel use.
• Good practice: keep the loom clipped properly, fix any oil or coolant leaks under the intake, use decent fuel, and follow the FSM procedure if testing or replacing.

Does a 2010 Subaru Legacy have a knock sensor, and how many?

Yes. The 2.5‑litre four‑cylinder models use one knock sensor on the block. The 3.6R H6 uses two sensors, one per bank. This is documented in the Subaru service literature and OEM parts listings for the BM/BR platform.

What are the symptoms of a bad knock sensor on this model?

Expect a check‑engine light (often P0325/P0327/P0328), reduced power as the ECU pulls timing, occasional pinging under load, and increased fuel use. Sometimes the car feels fine but logs a code — that’s why a scan at service time is handy.

Is it OK to keep driving with a faulty knock sensor?

It’ll usually run, but the ECU may go conservative, costing power and economy. More importantly, without accurate knock feedback, there’s a higher risk of detonation under hard use. Best bet: diagnose promptly and replace the sensor or repair the wiring as required.