Parts for your 2017 Subaru Impreza-Knock sensor

2017 Subaru Impreza knock sensor — purpose, fitment, and service advice

Technical sources including the Subaru Factory Service Manual for MY2017 Impreza (FB20 engine), OEM parts catalogues, and standard OBD-II diagnostics references confirm the 2017 Subaru Impreza is fitted with a knock sensor. It’s a core input for the ECU’s ignition control strategy on the 2.0‑litre FB-series boxer engine.

The knock sensor’s job is simple but critical: it “listens” for knock (detonation) via a piezoelectric element bolted to the engine block. When the sensor detects abnormal combustion, the ECU trims ignition timing and, if needed, enriches the fuel mix to protect the engine. That keeps the Impreza running smoothly on Aussie and Kiwi petrol grades, helping performance, economy, and engine longevity.

On the 2017 Impreza, the knock sensor is mounted to the cylinder block beneath the intake side. It’s a single-bolt fit with a dedicated 2‑pin connector. There’s no routine service interval for the sensor itself, but it’s wise to include quick checks during scheduled servicing: confirm the connector is secure, look for loom chafe, and ensure there’s no oil or coolant contamination around the mounting point. If it’s ever removed, the mating surface should be clean and dry, and the sensor reinstalled to the specified torque (around 24 N·m). Don’t over‑tighten, don’t use sealants, and don’t twist the body after torquing, as that can affect sensitivity.

Replacement is generally only required when faults arise. Typical signs include a check engine light with codes like P0325/P0327/P0328, reduced power, higher fuel use, or audible pinging under load. Before condemning the sensor, a technician should verify correct torque, inspect the harness and connector, and check for engine issues that cause real knock (e.g., poor fuel quality or heavy carbon build‑up). Using quality fuel and keeping the engine maintained (spark plugs on time, no vacuum leaks, proper cooling) reduces the chance of knock‑related problems.

When a new sensor is needed, a genuine or high‑quality equivalent matched to the FB20 is recommended. Fitment is typically straightforward with the intake side accessible, but battery disconnection, proper torque, and careful loom routing are essential. After installation, clear codes and confirm knock correction and learned values with a scan tool during a proper road test.

• Common fault clues: CEL with P0325/P0327/P0328, pinging under load, sluggish performance.
• Service tips: clean mounting face, correct torque (~24 N·m), secure connector, avoid grease/paint on the seat.
• Best practice: verify fuel quality and ignition system health before replacing the sensor.

Popular questions about the 2017 Subaru Impreza knock sensor

Where is the knock sensor on a 2017 Subaru Impreza?
It’s bolted to the engine block on the intake side of the FB20, beneath the manifold area. Access is from the top with intake components and covers out of the way. The sensor uses a single centre bolt and a 2‑pin plug.

What are the symptoms of a bad knock sensor?
Owners may see a check engine light (often P0325/P0327/P0328), feel reduced power, notice higher fuel consumption, or hear pinging under load. Because wiring or incorrect torque can mimic a failed sensor, a proper diagnostic check is important before replacement.

Can the car be driven with a knock sensor fault?
It will usually run, but the ECU may pull timing to protect the engine, which hurts performance and economy. Continued driving with real knock can damage the engine. Best to diagnose promptly—verify wiring, sensor torque, and fuel quality, then road test with a scan tool.