Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Circuit Description
Knock Sensor (KS) produces an output voltage (AC) based on mechanical engine vibration. PCM will retard the electronic spark timing on the signal being received. The amplitude and signal frequency is dependent upon the knock level. PCM will learn a minimum engine noise level at idle from the knock sensor and uses stored normal noise level calibration values for the rest of the RPM band. The knock sensor signal is only used during TDC combustion event of the firing cylinder. When in a combustion event, PCM filters the knock signal and compares it to normal calibration noise level for that RPM. If PCM determines that knock is present during the combustion event, it will retard timing on the next firing cylinders until knock is eliminated.
PCM will always try to work back to zero compensation level or no spark retard. DTC will set when PCM does not detect any normal engine noise for certain length of time and condition exists twice in one ignition cycle with engine speed between 1400-4000 RPM.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.