Parts for your 2020 Subaru Legacy-Knock sensor

2020 Subaru Legacy knock sensor: what it does and when to service it

Technical references confirm the 2020 Subaru Legacy is fitted with a knock sensor. Subaru’s factory service information (STIS) for the 2020 Legacy/Outback platform lists knock sensor diagnostics and DTCs (including P0325, P0327 and P0328), and the electronic parts catalogue lists a block-mounted knock sensor for both engines offered that year: the 2.5‑litre FB25 direct‑injection petrol and the 2.4‑litre turbocharged FA24. Subaru’s diagnostic procedures also describe its location on the cylinder block and outline ECM timing control based on knock feedback.

For anyone running a 2020 Subaru Legacy, the knock sensor is the quiet overachiever guarding the engine under the bonnet. Its job is to “listen” for knock (pinging) through a tuned piezo element and let the engine computer trim ignition timing to keep things smooth and safe. That means better performance on our local fuels, fewer rattles up hills, and long engine life over the kilometres.

When it goes on the fritz, the car usually makes it obvious: check‑engine light, flat performance, ordinary fuel economy, or pinging under load. Common fault codes include P0325, P0327 and P0328. The ECU will often pull timing as a protective move, so it’ll feel a bit doughy off the mark.

There’s no scheduled maintenance for the sensor itself, but a few habits help. Keep the wiring and connector clean and clipped, avoid soaking the area during engine washes, and fix oil or coolant weeps that can wick into the plug. If the intake comes off for other work, a quick visual check of the sensor’s mounting and harness is worthwhile.

Replacement is straightforward if access is planned. The sensor sits bolted to the top rear of the block beneath the intake manifold on both FB25 and FA24 engines. Disconnect the battery, remove intake ducting (and, if needed, the manifold), unplug the connector, and undo the single retaining bolt. Fit an OEM‑quality sensor, align the locating tab/orientation mark exactly as per the workshop manual, and tighten to the factory torque spec—over‑tightening or a wrong angle can give false readings. Don’t use sealants on the mating face. Reconnect, clear codes, and take a gentle drive so the ECU can relearn knock control. If knock codes come back quickly, check fuel quality, wiring continuity, and engine basics (vacuum leaks, carbon build‑up) before blaming the new sensor.

Handled properly, the Legacy’s knock sensor is a fit‑and‑forget part that helps the boxer engine stay lively and reliable on Aussie and Kiwi roads.

• Typical symptoms of a faulty knock sensor: CEL on, reduced power, higher fuel use, rattling under load.
• Best practice: use the correct sensor for your VIN, maintain proper orientation, and torque to spec.

FAQs

Where is the knock sensor on a 2020 Subaru Legacy?
It’s mounted on the top rear of the engine block under the intake manifold. Access usually means removing intake ducting, and in some cases lifting the manifold for clear spanner room.

Is it safe to drive with a bad knock sensor?
The car will usually run but with reduced power and higher fuel use as the ECU pulls timing. If real knock is occurring, prolonged driving can risk engine damage. Best to sort it promptly.

Do the 2.5 and 2.4T 2020 Legacy models use the same knock sensor?
Both engines use a block‑mounted knock sensor, but part numbers can differ. Match parts to your VIN and follow the factory orientation and torque specs during install.