Ignition and misfire

P0325Knock sensor 1 circuit malfunction, bank 1

Knock/Combustion Vibration Sensor A Circuit

Get it diagnosed soon

Generic OBD-II code

What the computer is measuring

Knock, also called detonation or pinging, is the fuel and air mixture igniting on its own ahead of the spark rather than burning smoothly outward from it. The two flame fronts collide, and the shock loads that produces will damage pistons, rings and bearings if it continues.

The knock sensor is essentially a microphone bolted to the engine block. It is a piezoelectric element that generates a small voltage when it is vibrated, and knock has a distinctive frequency signature the computer can pick out from ordinary engine noise. When it hears knock, the computer retards ignition timing until it stops, then creeps it back.

That feedback loop is worth more than it sounds. It lets manufacturers run more aggressive ignition timing than would otherwise be safe, because the computer can back off the instant it becomes a problem. More timing means more power and better economy.

P0325 is a circuit fault rather than a report of actual knock. The computer is not getting the signal it expects from the sensor circuit on bank 1. Without a working knock sensor it cannot detect detonation, so it does the only safe thing available and runs conservative timing all the time. That is why the common symptom is a car that feels slightly flat rather than one that sounds like it is coming apart.

Check the wiring before the sensor. On a lot of V engines the sensor sits in the valley under the intake manifold, which makes it an expensive part to replace and an easy connector to overlook.

What you will notice

  • Steady check engine light.
  • Reduced power, because the computer pulls ignition timing back as a precaution.
  • Slightly worse fuel economy.
  • Sometimes an audible pinging or rattling under load, if the engine is genuinely knocking.
  • Often no drivability change at all beyond the light.

Likely causes, most common first

Ordered by how often each one actually turns out to be the problem, not alphabetically and not by part price.

  1. A corroded or damaged sensor connector

    The most common cause. The sensor bolts to the engine block and its connector lives in heat and grime, and on many engines it sits under the intake manifold where it is rarely inspected.

  2. Chafed or broken wiring in the sensor harness

    The wire runs across a hot vibrating engine. Insulation hardens and rubs through against the block or a bracket.

  3. A failed knock sensor

    The sensor is a piezoelectric element, and it does fail. It is behind wiring in frequency, and on many engines replacing it means removing the intake manifold, so test before you commit.

  4. An incorrectly torqued sensor

    The sensor listens through the block, so it has to be tight to a specific torque against a clean surface. Loose, or with a washer that should not be there, it cannot hear properly.

  5. Genuine engine knock being detected

    Worth ruling in. Carbon build up, the wrong fuel grade, overheating or a lean condition can all make an engine actually knock.

What to check, in order

  1. Check what fuel the vehicle has been running and whether the engine has been overheating.

    Real knock from low grade fuel or an overheating engine is a different problem from a circuit fault, and it is worth eliminating before chasing wiring.

  2. Locate the sensor and inspect the connector and the visible wiring.

    Corrosion, a loose pin or chafed insulation explains the code, and repairing the harness is far cheaper than the sensor job on most engines.

  3. Measure the sensor resistance at the connector and compare it against the specification.

    An open or shorted reading confirms a failed sensor. A reading in specification moves the fault to the wiring or the computer.

  4. Check the harness for continuity and for a short to ground, back toward the computer.

    A wiring fault found here means the sensor does not need to come out at all.

  5. If the sensor is being replaced, confirm the mounting surface is clean and torque it to the exact specification.

    An incorrectly torqued new sensor sets the same code again, which is a common and frustrating repeat.

Where this one turns up most

  • V6 and V8 engines where the sensor sits in the valley under the intake manifold, so its wiring bakes and is never seen.
  • Higher mileage engines with original harnesses.

Codes that often show up alongside it

What a DriveDecode adapter can read

A DriveDecode adapter reads engine and emissions systems: the powertrain and emissions codes the OBD-II standard requires on every US vehicle it covers. It does not read ABS, airbag (SRS), TPMS or transmission-specific manufacturer codes. Those need make-specific decoding that generic OBD-II hardware cannot do.

Reading P0325 on your own car

DriveDecode pulls P0325 straight off the vehicle along with the freeze frame the computer stored when it set: the coolant temperature, engine load and speed at that exact moment. That context is what separates a fault that happens on a cold start from one that happens under load, and it is the first thing the list above asks you to narrow down.

See how DriveDecode works

Last reviewed 2026-09-05. Definition sourced from the published standard.