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Q: knock sensor on 2003 GMC Sierra 1500

Where is the knock sensor located, and is there more than 1?
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I have a 1999 4.8 vortec. There are two knock sensors under the intake manifold that are screwed into the lifter valley. The wires come out from under the rear of the intake manifold and connect the main wiring harness was at the rear of the intake manifold. Before you start taking off the intake check the wiring.
There is only one sensor. Located on the left rear top of engine block. Held on by a single bolt that goes through the middle of it.
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