Knock sensor: P0324, P0325, P0327, P0328
Lost power, higher fuel use, and a quieter engine under load? That is what a car looks like when it can no longer hear knock.
A knock sensor is essentially a microphone bolted to the cylinder block. It listens for the characteristic ringing and tells the control unit: «burning too late, pull the timing back». While it works, the engine keeps ignition on the edge of maximum power.
What happens when the sensor goes quiet
The unit cannot tell whether knock is present — so it does the only safe thing: retards the ignition with a margin. The engine stops knocking, but it also stops pulling.
That is why the symptom is deceptive: the car drives smoothly, nothing rattles, nothing overheats. It has simply gone sluggish and started drinking more. Many blame the fuel or the car's age.
What the codes mean
P0325, P0330 — sensor circuit. The first is for bank one, the second for bank two. An inline engine has one bank, a V engine two — and two sensors.
P0327, P0328 — signal below or above range. A low signal usually means an open circuit or a loose mount: the sensor only hears the block when torqued correctly.
P0324 — processing fault. The unit receives a signal but cannot interpret it.
What to look at in the app
There is no direct «knock level» in the mandatory OBD-II set. But there is ignition timing advance — and it answers the main question. On a warm engine under load the timing usually advances; if it stays retarded and never moves, the unit is running in protection mode.
Compare that with how the car feels: sluggish acceleration plus retarded timing — the picture adds up.
The common cause nobody looks for
The sensor is held by a single bolt with a specified torque. A loose bolt and the sensor stops hearing the block, although it is perfectly fine. After any repair where it was removed, check the torque before buying a new one.
What happens if you keep driving
By itself, nothing dramatic: the unit protects the engine. But if the sensor does not go silent and instead lies, the protection may not engage — and real knock destroys pistons in thousands of kilometres, not years. How it sounds and how it differs from other noises is covered by the symptom ringing under load.
