Parts for your 2020 Subaru Impreza-Knock sensor

2020 Subaru Impreza Knock Sensor — what it does and how to look after it

Yes, the 2020 Subaru Impreza is fitted with a knock sensor. This is confirmed by Subaru’s own technical documentation: the 2020MY Impreza Service Manual (Engine Diagnostics) lists DTCs P0327/P0328 for the knock sensor circuit, and the Subaru Genuine Parts Catalogue for the 2020 Impreza (engine group) shows a dedicated knock sensor for the FB20 engine. Workshop data services used across AU/NZ repairers likewise include test and replacement procedures for the Impreza’s knock sensor. So it’s absolutely relevant on this model.

On the 2020 Impreza, the knock sensor is a clever little microphone bolted to the engine block. Its job is to “listen” for knock (also called pinging or detonation) and tell the engine control module to tweak ignition timing and, if needed, fuelling. That way, the engine can safely run close to its sweet spot, keeping performance crisp and fuel use in check on everyday 91–95 RON petrol, even when conditions change — hot day under the bonnet, a steep hill, or a different fuel brand.

There’s no scheduled replacement interval for the knock sensor — it’s a fit-and-forget item unless it faults. As part of routine servicing, a technician will usually eyeball the area under the intake for wiring condition and make sure no oil or coolant leaks are soaking the sensor or its connector. If a warning light pops up with codes like P0327 or P0328, or the car feels flat and drinks more fuel than usual, the knock sensor circuit is one of the first places a workshop will check.

When replacing, it pays to stick with a quality OEM-equivalent part. The mating surface on the block should be clean, the sensor aligned correctly, and the retaining bolt tightened to the factory spec from the Subaru service manual — over-tightening or twisting the sensor can skew readings. Don’t paint it, don’t sand its face, and always route the harness so it won’t chafe. After fitting, clearing the code and doing a proper road test under load helps the ECU relearn.

• Telltales of trouble: check engine light, noticeable pinging under load, sluggish acceleration, poorer economy.
• Good habits: fix oil/coolant leaks promptly, keep connectors clean and fully seated, and use reputable fuel.
• Risk of ignoring it: the ECU may dial back power to protect the engine, and persistent knock can cause internal damage.

Technical references cited: Subaru 2020MY Impreza Service Manual (Engine/Diagnostics: Knock Sensor, DTC P0327/P0328), Subaru Genuine Parts Catalogue (2020 Impreza, Engine group: Knock Sensor for FB20).

Popular questions about 2020 Subaru Impreza knock sensors

Where is the knock sensor on a 2020 Subaru Impreza?
It’s mounted to the engine block beneath the intake area on the FB20 engine, roughly central on the block so it can “hear” all cylinders. Access usually requires removing upper intake components for a clear line to the sensor and connector.

What are the symptoms of a failing knock sensor?
Common signs include a check engine light (often with P0327 or P0328), reduced power as the ECU pulls timing, rough running under load, and a hit to fuel economy. In some cases you may hear pinging, but the ECU often masks it by retarding timing — you feel the power loss more than you hear the knock.

Does the knock sensor need regular servicing?
There’s no routine replacement interval. During normal services it’s wise to inspect the connector and nearby wiring, and keep the area free of oil and coolant. Replace the sensor only if testing confirms a fault, after replacement, follow the factory torque and orientation procedure and verify with a road test.