Parts for your 2012 Subaru Impreza-Knock sensor

2012 Subaru Impreza knock sensor — what it does and how to look after it

Yes, the 2012 Subaru Impreza is fitted with a knock sensor. Technical references confirming this include the Subaru Factory Service Manual for the 2012MY Impreza (GJ/GP), which details a “Knock Sensor” in the Engine Diagnostics section with DTCs P0325–P0328, and the Subaru parts catalogue for the FB20 2.0‑litre engine, which lists a dedicated knock sensor assembly. Subaru service information also specifies installation torque and orientation for the sensor on the FB-series block beneath the intake manifold.

On this Impreza, the knock sensor is a small piezoelectric microphone bolted to the top of the engine block, tucked under the intake manifold. Its job is to “listen” for pinging (detonation) and feed that signal to the ECU. When the ECU hears knock, it trims ignition timing and, if needed, enriches fuel to protect the engine. That lets the FB20 run efficiently on Aussie and Kiwi pump fuels without risking damage when conditions get a bit hot or load gets heavy.

It’s not a routine service item, but it does deserve attention during major services or when the check engine light pops up. Typical clues that the knock sensor or its wiring isn’t happy include a rattly, metallic ping under load, sluggish performance, poor fuel economy, or fault codes like P0325, P0326, P0327, or P0328.

• Visual check: During a scheduled service, a quick look under the bonnet for brittle wiring, oil contamination, or a loose mounting bolt is worthwhile.
• Replacement: If diagnostics confirm a faulty sensor, fit a quality OEM‑spec unit. The mounting face must be clean and dry, and the bolt torqued to about 24 N·m. Over‑tightening or the wrong angle can make the sensor read rubbish.
• Orientation: Follow the Subaru procedure for sensor clocking on the FB20. Getting the angle wrong can cause false knock or missed events.
• Aftercare: Clear codes, road test under load, and check for learned knock correction values with a scan tool to confirm the fix.

Owners planning DIY work should disconnect the battery, let the engine cool, and expect tight access under the intake. Many workshops remove the air ducting for room. When set up correctly, the knock sensor quietly keeps timing optimised so the Impreza feels crisp and stays reliable for the long kilometres ahead.

Popular questions

Where is the knock sensor on a 2012 Subaru Impreza?
It sits on the top of the FB20 engine block under the intake manifold area, roughly central. Access is usually from above by removing the air intake ducting, on some jobs the throttle body or manifold may be loosened for better reach.

What codes point to a bad knock sensor on this model?
Common diagnostic trouble codes are P0325 (circuit fault), P0326 (range/performance), P0327 (low input), and P0328 (high input). Before replacing the sensor, check the connector, harness routing, and mounting torque/angle, as these often cause false faults.

Can driving with a faulty knock sensor damage the engine?
The ECU may run very conservative timing to protect things, so power and economy drop. If actual knock isn’t being detected, prolonged heavy load could risk engine damage. It’s best to sort it promptly to keep the FB20 safe and sprightly.