Engine internals
Knock sensor
Listens for uncontrolled combustion so timing can back off.
Bolted to the side of the engine block between cylinders.
A piezoelectric element converts block vibration into a signal the DME filters for knock frequencies.
A doctor’s stethoscope pressed to the block.
Reduced power or a knock-control fault may follow sensor, wiring or fuel-quality problems.
Usually condition-based rather than a routine replacement. Lubrication, overheating and the exact engine affect wear.
Internal-engine work is usually labor-intensive. Diagnosis and the engine code determine the repair scope.
BMW turbo engines use knock control on every cylinder to run close to the limit safely.
BMW petrol and diesel engines; petrol-only systems are identified individually.
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