2004 Avalanche, 5.3 with 241K miles. My CEL came on two months ago, traced it to a knock sensor. Mechanic replaced the KS and the wiring harness. CEL came back on a few weeks later. This time the other side KS is throwing the CEL. Mechanic went back in, replaced the other KS, and its wiring. Drove it and next day CEL came back on, still indicating KS. Mech reset the CEL. Drove it next day, and CEL comes on again. My mech is baffeled. He does not know what to do next, except reset the CEL. Can anyone offer help? Thanks!
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Knock sensors CEL won't clear
- Thread starter gfh77665
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ygmn
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Is there not a LEARN procedure for the Knock Sensor?
Or maybe that is Crank Sensor?
Best thing is to find GM instructions for 5.3 engine on what to troubleshoot for that code.
Or maybe that is Crank Sensor?
Best thing is to find GM instructions for 5.3 engine on what to troubleshoot for that code.
Definitely Knock sensors.
O2 was replaced a few months ago.
My mechanic did it, so I don't know. I would guess he did not use ACDelco.
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- Jan 29, 2022
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I replaced my knock sensors (rear was throwing the code) and harness. I also followed several recommendations to remove the rear foam blocker under the manifold (which holds water that may get under the manifold and prevents it from draining out) and seal the rubber grommets that cover the knock sensors ( the grommets alone are not water tight). I cleared the codes with the OBD Scanner. The Code came back once for the forward code. I cleared it though the OBD scanner. Then I drove the truck uphill, loaded and the codes came back. I had a mix of low and midrange octane gas in the tank at the time. Since then, I have put only 91 or 93 in it and so far, no more codes. I have not driven it "hard" though. No heavy loads.
2003VAAV
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Gg05 has good advice, I would verify with your mechanic what brand he used. The KS system is sensitive, it's one of those "things" that I would stick with ACDelco even if the parts cost more.
This knock sensor (KS) system uses one or 2 broadband one-wire sensors. The sensor uses piezo-electric crystal technology that produces an AC voltage signal of varying amplitude and frequency based on the engine vibration, or noise, level. The amplitude and frequency are dependant upon the level of knock that the KS detects. The control module receives the KS signal through a signal circuit. The KS ground is supplied by the engine block through the sensor housing.
One way the control module monitors the system is by output of a bias voltage on the KS signal wire. The bias voltage creates a voltage drop that the control module monitors and uses to help diagnose KS faults. The KS noise signal rides along this bias voltage, and due to the constantly fluctuating frequency and amplitude of the signal, will always be outside of the bias voltage parameters.
Another way the control module monitors the system is by learning the average normal noise output from the KS. The control module learns a minimum noise level, or background noise, at idle from the KS and uses calibrated values for the rest of the RPM range. The control module uses the minimum noise level to calculate a noise channel. The control module uses this noise channel, and the KS signal that rides along the noise channel, in much the same way as the bias voltage type does. As engine speed and load change, the noise channel upper and lower parameters will change to accommodate the normal KS signal.
In order to determine which cylinders are knocking, the control module only uses KS signal information when each cylinder is near top dead center (TDC) of the firing stroke. If the control module has determined that knock is present, it will retard the ignition timing to attempt to eliminate the knock. The control module will always try to work back to a zero compensation level, or no spark retard. An abnormal KS signal will fall within the noise channel or will not be present. KS diagnostics are calibrated to detect faults with the KS circuitry inside the control module, the KS wiring, or the KS voltage output.
This knock sensor (KS) system uses one or 2 broadband one-wire sensors. The sensor uses piezo-electric crystal technology that produces an AC voltage signal of varying amplitude and frequency based on the engine vibration, or noise, level. The amplitude and frequency are dependant upon the level of knock that the KS detects. The control module receives the KS signal through a signal circuit. The KS ground is supplied by the engine block through the sensor housing.
One way the control module monitors the system is by output of a bias voltage on the KS signal wire. The bias voltage creates a voltage drop that the control module monitors and uses to help diagnose KS faults. The KS noise signal rides along this bias voltage, and due to the constantly fluctuating frequency and amplitude of the signal, will always be outside of the bias voltage parameters.
Another way the control module monitors the system is by learning the average normal noise output from the KS. The control module learns a minimum noise level, or background noise, at idle from the KS and uses calibrated values for the rest of the RPM range. The control module uses the minimum noise level to calculate a noise channel. The control module uses this noise channel, and the KS signal that rides along the noise channel, in much the same way as the bias voltage type does. As engine speed and load change, the noise channel upper and lower parameters will change to accommodate the normal KS signal.
In order to determine which cylinders are knocking, the control module only uses KS signal information when each cylinder is near top dead center (TDC) of the firing stroke. If the control module has determined that knock is present, it will retard the ignition timing to attempt to eliminate the knock. The control module will always try to work back to a zero compensation level, or no spark retard. An abnormal KS signal will fall within the noise channel or will not be present. KS diagnostics are calibrated to detect faults with the KS circuitry inside the control module, the KS wiring, or the KS voltage output.