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Testing the Knock Sensor in Your Car

Model: Subaru Forester SF, MK 1 - Years 1997-2002
Part: Checks and maintenance

The knock sensor detects if the combustion of the air-fuel mixture in the engine cylinders occurs incorrectly, that is, under detonation conditions. Detonation can be caused by excessively high pressure/temperature or by using fuel with an inappropriate octane number, leading to reduced engine performance and severe physical damage to the cylinders. A test on the engine control unit determines which cylinder experienced detonation through the signals emitted by the knock sensors. The reaction is a reduction in pressure in the cylinder through a change in the mixture enrichment.

Updated on 21 February 2026 by ScegliAuto

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