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P0328 — Knockcombustion Vibration Sensor Circuit High

Generic OBD-II · all makesPowertrain (engine & transmission)

OBD-II code P0328 indicates that the knock sensor circuit is reporting a voltage higher than the manufacturer's expected range. This typically means the sensor signal is shorted to a voltage source, the sensor is internally faulty, or there is excessive mechanical noise causing a continuous high output. The engine control module (PCM) sets this code when it detects the abnormal signal, which can lead to ignition timing being retarded to protect the engine.

Symptoms

What causes it — most likely first

1. Faulty knock sensor

The piezoelectric element inside the sensor can fail, causing it to output a constant high voltage or short internally. This is the most common cause of a P0328 code.

2. Wiring harness short to voltage

The signal wire from the knock sensor may be chafed or pinched, contacting a power source and pulling the circuit voltage high. This can occur anywhere between the sensor and PCM.

3. Poor electrical connection at the sensor

Corrosion, a loose connector, or damaged terminals at the knock sensor can create high resistance or intermittent contact, leading to an abnormal voltage reading.

4. Excessive engine mechanical noise or vibration

Severe engine knock, loose components, or abnormal vibrations can cause the knock sensor to generate a continuous high-frequency signal that the PCM interprets as a circuit fault.

5. Faulty PCM (rare)

Internal damage to the PCM's knock sensor input circuit can cause a false high-voltage reading, but this is the least likely cause and should only be considered after all other possibilities are ruled out.

How it's diagnosed

  1. Visually inspect the knock sensor, its connector, and the wiring harness for obvious damage, corrosion, or loose connections.
  2. Check the sensor's internal resistance with a multimeter and compare to the manufacturer's specification; an open or shorted sensor indicates replacement.
  3. Use a scan tool to monitor knock sensor voltage or signal while tapping the engine block near the sensor; a functioning sensor should produce a brief voltage spike.
  4. Inspect the wiring between the sensor and PCM for shorts to voltage, open circuits, or high resistance using a wiring diagram and multimeter.
  5. Evaluate for engine mechanical issues such as excessive knock, loose brackets, or worn components that could cause false sensor activation.
  6. If all other tests pass, perform a PCM self-test or swap with a known-good unit only as a last resort, after confirming no wiring or sensor faults.

Code facts & related codes

SystemPowertrain (engine & transmission)
StandardizationSAE generic — identical on every make
Related codesP0320 — Ignitiondistributor Engine Speed InputP0321 — Ignitiondistributor Engine Speed InputP0322 — Ignitiondistributor Engine Speed InputP0323 — Ignitiondistributor Engine Speed InputP0324 — Knockcombustion Vibration Control SystP0325 — Knockcombustion Vibration Sensor Circu

Frequently asked

Can I drive my vehicle with a P0328 code?

Short-distance driving is usually safe, but the engine may run with retarded timing, reducing power and fuel economy. Prolonged driving could risk engine damage if actual knock occurs and is not detected.

Is the knock sensor easy to replace?

It depends on the vehicle. On some engines the sensor is easily accessible, while on others it may be buried under the intake manifold or other components, requiring significant labor.

Do I need to replace the PCM for a P0328 code?

No, the PCM is very rarely the cause. Many drivers are mistakenly told to replace the computer, but the fault is almost always with the sensor, wiring, or connector. Always diagnose those first.

What happens if I ignore this code?

The engine will likely continue to run with reduced performance and efficiency due to retarded ignition timing. If the sensor is not functioning, the PCM cannot detect real knock, which could lead to engine damage over time.