P0328 means the engine control module has detected the knock sensor circuit’s signal voltage reading consistently too high, a more specific electrical signature than our P0325 (general knock sensor circuit malfunction) guide, which covers the broader category of knock sensor circuit faults without narrowing down to a particular voltage direction. A code narrowed to “high input” specifically points a technician more directly toward a short to power or a wiring fault than the wider range of possibilities P0325 alone would suggest.
What Does P0328 Mean?
The knock sensor detects abnormal vibration in the engine block consistent with detonation (“knock”), allowing the control module to retard ignition timing slightly to protect the engine when it senses this condition. P0328 specifically means the circuit’s voltage signal is reading higher than the expected range — a more precise finding than the general circuit malfunction covered in our P0325 guide, which is stored when a fault is detected but doesn’t necessarily point to a specific high or low voltage direction. This extra specificity is genuinely useful diagnostically, since a “high input” fault points more directly at a short to a power source or a specific wiring problem.
Common Symptoms
- Check engine light on
- Reduced power or performance, since the control module may retard timing more conservatively than necessary in response to unreliable knock sensor data
- Reduced fuel economy in some cases
- No noticeable drivability symptom at all in many cases, beyond the warning light
Common Causes, Most Likely First
- A wiring fault causing a short to a power source somewhere along the knock sensor’s circuit, which is the most direct explanation for a signal reading persistently too high.
- A damaged or corroded connector at the knock sensor itself, allowing unintended voltage to bleed into the signal circuit.
- A failing knock sensor itself, with an internal fault causing it to output an abnormally high signal regardless of actual engine vibration.
- A wiring harness routed too close to a high-voltage source elsewhere in the engine bay, inducing unwanted voltage into the knock sensor circuit.
How to Diagnose It
- Inspect the knock sensor’s wiring and connector for damage, corrosion, or signs of contact with another wire or a power source.
- Test the knock sensor’s output voltage with a multimeter or oscilloscope against the manufacturer’s specification to confirm whether the sensor itself or the wiring is at fault.
- Check for the sensor’s wiring routing near other components, since a chafed wire contacting a power source is a common and fixable cause.
- Compare with our P0325 guide if you’re unsure which knock sensor code applies to your situation — P0328 specifically narrows to a high-voltage signature.
Never work under a vehicle supported only by a jack. Use axle stands on firm, level ground, chock the wheels that stay down, and leave the car in gear or Park with the handbrake on. A jack lifts; stands hold.
Possible Fixes
| Cause | Fix | Typical cost |
|---|---|---|
| Wiring short to power | Repair the wiring | $100 – $250 |
| Damaged/corroded connector | Clean or replace the connector | $50 – $150 |
| Failing knock sensor | Replace the knock sensor | $150 – $350 |
Can I Keep Driving With This?
Yes, generally — a knock sensor circuit fault on its own doesn’t create an immediate safety issue, though it’s worth addressing since the engine may run a more conservative, less efficient timing strategy than necessary while the fault is present. No urgency from a drivability standpoint.
When to See a Mechanic
Not urgent — a straightforward diagnostic and repair at most shops. More in our trouble codes section.
Frequently Asked Questions
What does P0328 mean?
It means the knock sensor circuit’s signal voltage is reading consistently too high — a more specific electrical finding than the general P0325 knock sensor circuit malfunction code.
Is P0328 the same as P0325?
P0328 is a more specific version of the same underlying system — P0325 is the general circuit malfunction code, while P0328 narrows it down to a high-voltage signal specifically.
What’s the most common cause of P0328?
A wiring fault causing a short to a power source somewhere along the knock sensor’s circuit is the most direct explanation for a persistently high signal reading.
Is it safe to drive with a P0328 code?
Yes, generally — it doesn’t create an immediate safety issue, though the engine may run a slightly less efficient, more conservative timing strategy while the fault is present.
How much does it cost to fix P0328?
Often $100–$250 for a wiring repair, up to $350 if the knock sensor itself needs replacement.
