Parts for your 2015 Subaru Forester-Knock sensor

2015 Subaru Forester knock sensor — what it does and how to look after it

Yes, the 2015 Subaru Forester uses a knock sensor across both engine options (2.5i FB25 and 2.0XT FA20F). Factory technical information lists the knock sensor as a monitored component with dedicated fault codes (P0325, P0327, P0328), and it appears as a serviceable part in Subaru’s parts catalogues and mainstream repair databases.

• Subaru factory service information (2015MY Forester Engine/Diagnostics) — Knock Sensor Circuit: DTC P0325/P0327/P0328
• Subaru parts catalogues for 2015 Forester — Knock Sensor listed as a replaceable component
• Professional repair manuals (e.g., Haynes/Chilton, and trade databases like Alldata/Mitchell1) — testing and replacement procedures for the knock sensor on 2015 Forester engines

On this Forester, the knock sensor is a piezoelectric microphone bolted to the engine block under the intake area. Its job is to “listen” for combustion knock (pinging) and report it to the ECU. The ECU then trims ignition timing (and on the turbo, can also temper boost) to protect the engine while keeping fuel economy and performance on song. It’s one of those quiet heroes that lets the vehicle run happily on day-to-day Aussie and Kiwi petrol without drama.

There’s no scheduled replacement interval for the knock sensor, it’s a fit-and-forget item unless it fails or is damaged. Tell-tales of trouble include a check engine light, stored codes P0325/P0327/P0328, sluggish performance, rattly pinging under load, or a fuel economy drop. Because the sensor reads minute vibrations, correct mounting and wiring are crucial. If it needs replacing, use quality parts, fit it to a clean, dry, unpainted pad on the block, route the harness in the factory path, and torque it to the Subaru spec from the workshop manual. Over-tightening, under-tightening or flipping the sensor the wrong way can all skew readings.

As part of regular servicing, it’s smart to:

• Visually check the sensor and plug for oil contamination, heat damage or brittle wiring
• Avoid pressure-washing the engine bay around the sensor and connectors
• Use the recommended fuel octane (FB25 2.5i: follow the owner’s manual, FA20F 2.0XT turbo: premium unleaded 95/98 RON)
• Address intake leaks and misfires quickly, as they can trigger knock events and false codes

If a fault code appears after replacement, clear it with a scan tool, perform a proper road test, and let the ECU complete its learning. When fitted and torqued correctly, the knock sensor keeps the 2015 Forester feeling smooth, responsive and protected across thousands of kilometres.

Does the 2015 Subaru Forester have a knock sensor?
Yes. Both the 2.5i (FB25) and 2.0XT (FA20F) engines use a block-mounted knock sensor. It feeds the ECU so timing and, on the turbo, boost can be adjusted to prevent engine knock and protect the hardware.

Where is the knock sensor on a 2015 Forester?
It’s bolted to the engine block under the intake area, roughly central on the block. Access is typically from above with the intake ducting removed. Always refit it to a clean pad and torque to factory spec for accurate readings.

Is it safe to drive with a knock sensor fault (P0325/P0327/P0328)?
The vehicle will usually run, but power might be reduced and fuel use may increase. More importantly, genuine knock may go unchecked, which risks engine damage. It’s best to diagnose promptly — check wiring, connector condition, mounting torque and, if needed, replace the sensor.