Engine internals

Knock sensor

Listens for uncontrolled combustion so timing can back off.

Drag to turn it Open in the 3D lab
Where it sits

Bolted to the side of the engine block between cylinders.

How it works

A piezoelectric element converts block vibration into a signal the DME filters for knock frequencies.

Think of it as

A doctor’s stethoscope pressed to the block.

Symptoms when it fails

Reduced power or a knock-control fault may follow sensor, wiring or fuel-quality problems.

Lifespan

Usually condition-based rather than a routine replacement. Lubrication, overheating and the exact engine affect wear.

Repair cost

Internal-engine work is usually labor-intensive. Diagnosis and the engine code determine the repair scope.

The BMW angle

BMW turbo engines use knock control on every cylinder to run close to the limit safely.

Used in

BMW petrol and diesel engines; petrol-only systems are identified individually.

Sources
Same system

Engine internals

Engine blockHolds the cylinders and supports the engine’s rotating parts.Cylinder headCloses the cylinders and carries the valves that control breathing.Cylinder-head gasketSeals combustion pressure, oil and coolant between the block and head.PistonReceives combustion force and moves up and down inside a cylinder.Piston ringsSeal combustion gas and control the oil film on cylinder walls.Connecting rodTransfers piston force to the crankshaft.CrankshaftTurns the pistons’ back-and-forth motion into rotation.Crankshaft main bearingSupports the crankshaft on a controlled film of oil.