P0328 on Subaru
Knock Sensor 1 Circuit High Input (Bank 1)
P0328 on Subaru vehicles indicates knock sensor 1 circuit high input (bank 1). Au7o has documented this code across 1 Subaru model — most commonly on Forester. This code means the knock sensor on engine bank 1 produced a voltage signal higher than its normal expected range. The knock sensor detects the vibrations of engine knock (detonation) so the computer can pull back ignition timing and protect the engine from damage. A high-input reading typically indicates an electrical issue such as a short to voltage or a wiring/connector fault, rather than genuine, sustained knock. While the sensor is faulted, the engine may default to conservative timing, slightly hurting performance and fuel economy. Typical repair costs on Subaru range from $80 to $250, depending on the specific model and root cause.
Common Causes of P0328
- •Faulty knock sensor (Bank 1, Sensor 1)
- •Sensor wiring shorted to voltage or power
- •Damaged or corroded sensor connector
- •Loose or improperly torqued sensor mounting
- •Chafed/pinched wiring harness
- •Grounding or shielding fault in the circuit
- •Faulty engine control module (PCM) — rare
P0328 on Subaru by Model
Subaru Forester(1 issue)
- Knock Sensor Housing Cracking — P0325 and Permanent Timing Retard1998-2005
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.
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View P0328 across all makes →Frequently Asked Questions
What does P0328 mean on Subaru?▼
P0328 stands for "Knock Sensor 1 Circuit High Input (Bank 1)." This code means the knock sensor on engine bank 1 produced a voltage signal higher than its normal expected range. The knock sensor detects the vibrations of engine knock (detonation) so the computer can pull back ignition timing and protect the engine from damage. A high-input reading typically indicates an electrical issue such as a short to voltage or a wiring/connector fault, rather than genuine, sustained knock. While the sensor is faulted, the engine may default to conservative timing, slightly hurting performance and fuel economy. On Subaru specifically, this code is documented across 1 model.
What causes P0328 on Subaru vehicles?▼
Common causes on Subaru: Faulty knock sensor (Bank 1, Sensor 1), Sensor wiring shorted to voltage or power, Damaged or corroded sensor connector, Loose or improperly torqued sensor mounting, Chafed/pinched wiring harness. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0328 on a Subaru?▼
Repair costs on Subaru range from $80 to $250, depending on the specific model and root cause.
Which Subaru models have P0328 documented?▼
Au7o has documented P0328 on 1 Subaru model: Forester.