Knock Sensor Operation. How Do They Work?

[andyems]

I was hoping someone on here could help me out with how the spark knock sensors actually do their job? I have a GMT-900 '07 Silverado with the 5.3L. It only has 20,500 miles but it's coming up to the 3 year mark on the warranty.

Anyway, I hear what seems to be a spark knock sometimes, mainly when it starts in the first few minutes. Sometimes I hear it other times, but seems to be more prevalent when I pull it in to drive or reverse after cold start. It either always goes away, or I just don't notice it, because by the time I get where I'm going, it seems to be gone. I was using name brand 87 octane at the time, but still had it when I went up to 89, again only intermittently. I didn't know if a bad knock sensor would throw a code or not, but I don't have, or have ever had a code show up and otherwise the truck runs great.

I DO have the Hypertech programmer installed in the 87 setting, and still use the 89 octane. I've only had this programmer for the last 4 weeks, and the noise has been there since I bought it 2 years ago, so it was present way before the Hypertech programming.

I have no idea how a spark knock sensor actually work or what it does to quiet things down. Do they take a while to do their thing, maybe to war, up or something? Thought it's something that takes time to get working, and what I hear is the knock before they can start doing their thing, and when they get warmed up, they then do their job or should they immediately begin to work.

I know I've had this truck for 2 years and it's a little late to be getting this fixed, but I'm getting married in Oct and the time has really krept up on me with all this wedding stuff the last few months. Want to take care of this before Oct 1 when the warranty goes out unless this is something normal. The dealer is an hour away, and don't want to waste a whole day for them to tell me this is something normal. Thanks in advance for the help.

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There's nothing wrong with what you're describing, that's a normal startup knock. And the knock sensors work right away, although when they're warm, they're more sensitive. They just change resistance when it feels a srong enough vibration, kinda of like a car alarm shock sensor, but less sensitive.