Can I drive with a bad knock sensor? Technically, yes. In most cases you’ll just have a check engine light and a code. V engines will typically have more than one knock sensor.
Located on the cylinder head, intake manifold, or engine block, the knock sensor functions as an ear to your car’s computer, picking up unusual vibrations caused by engine detonation.
Engine control algorithms are very precise in sorting out spurious noises from actual engine knocks due to detonation (early combustion that impacts the piston on its way up).
Typical knock sound can be heard within the frequency spectrum of between 5 and 7 kHz, depending on the cylinder bore. The ECM filters out all other frequencies and only reacts to detonation based knocking.
–Richard McCuistian, ASE Certified Master Automobile Technician
Typical knock sound can be heard within the frequency spectrum of between 5 and 7 kHz, depending on the cylinder bore. The ECM filters out all other frequencies and only reacts to detonation based knocking.
Because there can be other engine vibrations in this same frequency range, the measurement is ignored if it isn’t between 70° before TDC and 10° after TDC. This window is wider on some platforms so that a loose knock sensor can cause issues.
Inside the knock sensor is a piezo ceramic disc that produces a voltage when placed under pressure. The seismic weight of a detected engine knock reacts with the ceramic disc and creates pressure waves that generate voltage spikes from the sensor to the ECM.
But again, remember that only the “knock” noises that fall within a few degrees before the proper cylinder combustion windows will trigger the engine control module to retard the ignition timing. With coil-on-plug ignition, the ECM can retard the timing on just one cylinder or any number of others separately. If the ECM responded to every knocking noise spike generated by the sensor (which it doesn’t), it would be a disaster.
In conclusion, you can drive with a bad knock sensor, but if you begin to feel problems in the way the engine sounds, runs, or performs, scan for codes or have it checked to see if you get knock sensor DTCs.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.
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BS, I have a front and rear knock sensor. rear went bad 50K miles ago. I now have 282,000 miles on the truck and don't notice one difference
Hi Keith,
The side effects of a bad knock sensor will depend largely on the year, make, and model of your vehicle. On all vehicles built after 1996, a bad knock sensor will almost always turn on the check engine light, which will result in a failed emissions inspection (if you live somewhere that requires such an inspection).