On a Subaru, P0328 is the generic OBD-II code for Knock Sensor 1 Circuit High Input (Bank 1 or a single sensor). It means the engine control module (ECM) or powertrain control module (PCM) has detected a knock-sensor circuit signal higher than expected. The code points to a circuit condition; by itself, it does not prove the sensor has failed, that the engine is actually knocking, or that a particular repair is needed.
The knock sensor sends the engine computer a signal used to detect vibration associated with engine knock. A fault in that signal can affect the computer’s ability to monitor knock, but diagnosis is needed to find the cause. A general P0328 diagnostic guide also stresses checking the circuit rather than assuming the sensor is the only possible fault.
What does P0328 mean on a Subaru?
“Circuit high input” describes the signal detected by the computer. It is not a direct measurement confirming engine detonation, and it does not identify a failed component on its own. A faulty sensor is one possibility, but a connector, wiring, or other circuit problem can also produce a high input. The code description is also used in general explanations of P0328 and the knock-sensor circuit.
Some vehicles with P0328 may show only a check-engine light. Others may have symptoms such as pinging or knocking under acceleration, reduced power, or changes in drivability. These symptoms do not confirm that the sensor is faulty—or that the engine is knocking. It is also possible to have the code without noticing any change in how the car runs.
What can cause P0328, and how is it diagnosed and fixed?
Possible causes include a faulty knock sensor, a poor electrical connection, a corroded connector, damaged wiring, an open or shorted harness, or another fault in the circuit. If the car also runs poorly or makes an abnormal noise, a technician may need to check for a separate underlying engine or fuel-related issue. The code alone does not establish that such a problem is present.
A sensible diagnosis checks the fault before parts are replaced:
- Read all stored codes and available freeze-frame data. Freeze-frame information can help show the conditions recorded when the fault was detected. Other codes may help direct the investigation.
- Inspect the relevant connector, wiring, and grounds. Look for visible damage, corrosion, or a loose connection. A visual check can reveal some problems, but it cannot rule out an electrical fault.
- Test the sensor and circuit using the correct Subaru service information. Test steps and specifications must match the vehicle’s year, engine, and configuration. Do not rely on a generic resistance figure or online test procedure as a Subaru pass/fail specification.
- Repair the fault that testing confirms. That could mean repairing a verified wiring or connector problem, or replacing the sensor if it has been tested and found faulty. A control-module fault should not be assumed; module replacement needs supporting test results and the applicable service information.
- Clear the code and check whether it returns. A repair should be verified rather than judged solely by whether the warning light goes out immediately.
A P0328 diagnostic and repair overview discusses inspection and circuit-related possibilities, but it is not a substitute for Subaru service information for the exact vehicle. If electrical testing or access to the sensor is beyond your equipment or experience, ask a qualified technician to diagnose it. Replacing the knock sensor solely because P0328 is stored can waste money if the fault is elsewhere.
Does P0328 mean the same thing on an Outback, Impreza or Forester?
The general P0328 description applies to the knock-sensor circuit, but the available information does not establish the same sensor location, parts, access requirements, causes, or test specifications for every Outback, Impreza, or Forester. A source discussing a particular Forester application should not be treated as instructions for all Forester generations or for other Subaru models.
For a vehicle-specific diagnosis, provide the model year, engine, all stored codes, and the symptoms. Use service information that matches that exact vehicle before identifying a sensor or choosing a test procedure.
Where is the knock sensor on a Subaru?
Knock sensors are commonly described as being mounted on the engine block or in the intake-manifold area, but that is only a general description—not a verified location for every Subaru. The sensor arrangement, bank identification, and access can depend on the engine. Confirm the location and the correct sensor using the vehicle-specific service manual or a qualified technician before buying parts or beginning work; do not rely on a generic video for Subaru-specific removal or installation instructions.
How much does it cost to fix P0328?
There is no verified Subaru-specific parts price, labour time, or repair estimate in the available research, so a reliable dollar figure cannot be given here. The total bill depends on what diagnosis finds: a sensor, connector, or wiring fault, or another circuit issue. The vehicle and engine, part choice, sensor access, diagnostic time, labour, and local shop rates can all affect the price.
The sensor’s purchase price is not the same as the complete repair cost, which may include diagnosis and labour. Ask for an itemised estimate based on the confirmed fault before authorising replacement—particularly if a quote includes control-module replacement without test results explaining why it is needed. A dependable estimate requires the vehicle’s year and engine, your location, and a diagnosis.
Can you drive a Subaru with P0328?
The code alone cannot establish that a particular Subaru is safe to drive, and it does not establish that continued driving will cause damage. If the car has an isolated code and no noticeable symptoms, arrange prompt diagnosis rather than treating the absence of symptoms as proof that everything is safe.
If you hear persistent pinging or knocking, notice power loss or worsening drivability, stop in a safe place and seek professional assessment instead of continuing to put the engine under load. Do not continue driving if the check-engine light is flashing, the engine is running badly, or severe knocking is present; arrange roadside assistance or help from a technician. Follow any other vehicle warnings. For broader dashboard context, see what a Subaru check-engine light and flashing cruise control can mean.
Is P0328 serious?
Its seriousness depends on the underlying cause and what the vehicle is doing. P0328 is not, by itself, proof of catastrophic engine damage, but it is not proof that the car is harmless to drive either. An isolated code still needs diagnosis; persistent knocking or pinging, loss of power, or worsening running makes prompt assessment more important. Testing is needed to distinguish an electrical circuit fault from actual engine knock or another engine problem.