P0325 on Subaru: How to Diagnose & Fix
Knock Sensor 1 Circuit Malfunction (Bank 1)
1 Subaru model · 1 documented issue · $80-$250 repair
P0325 on Subaru by model: symptoms, diagnosis and fix
The single knock sensor bolted to the top of the EJ block on SF- and early SG-generation Foresters has a brittle plastic/resin housing that cracks after years of heat cycling directly on the block. Once cracked, the piezo element's circuit reads out of range and the ECU sets P0325. The car keeps running, but the ECU falls back to a conservative safe ignition map: owners report noticeably reduced power, sluggish throttle response and a measurable drop in fuel economy. The failure is common enough that many independent shops replace the sensor on any high-mileage EJ Forester showing that code without further diagnosis. A secondary cause is the sensor wiring harness chafing or the connector corroding, so the harness should be inspected before condemning the sensor.
Common Symptoms
- Check engine light with P0325
- Reduced power and sluggish acceleration
- Worse fuel economy
- Engine feels flat under load
- Code returns shortly after a replacement sensor is overtightened
How to Fix
Replace the knock sensor — it sits on top of the block under the intake manifold and is reachable with a 12mm socket and extensions, typically about 30-60 minutes of work. Torque matters: overtightening cracks the new sensor's housing and brings the code straight back, so use the specified low torque value and do not impact it on. Inspect the harness pigtail and connector for green corrosion or chafe damage at the same time, and clear the code and confirm the ECU returns to normal timing. Parts are inexpensive. No recall or warranty extension applies.
Sources for this issue (3)
P0325 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0325 mean on a Subaru?
P0325 stands for "Knock Sensor 1 Circuit Malfunction (Bank 1)." This code indicates a fault in the knock sensor 1 circuit on Bank 1. The knock sensor listens for the vibrations of detonation (pinging/spark knock) and lets the computer retard ignition timing to protect the engine. When the sensor's signal is missing, out of range, or the circuit is open/shorted, P0325 sets. With knock detection compromised, the computer may run more conservative timing, causing reduced power and slightly lower fuel economy, and the engine is less protected against damaging knock. On Subaru it is documented across 1 model: Forester.
What are the most common causes of P0325?
The most common causes of P0325 are: Failed knock sensor, Corroded or loose knock sensor connector, Damaged, open, or shorted sensor wiring, Improperly torqued or loosely mounted sensor, Moisture or corrosion in the connector, Wiring harness chafing near the engine, Faulty PCM/ECM (rare). The specific cause varies by vehicle.
How much does it cost to fix P0325 on a Subaru?
Published repair estimates on Subaru range from $80 to $250 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.