Check engine lite code says knock sensor fault.Tell me more
about this on 2004 GMC Sierra 1500

Let me know how important the knock sensors are i know they are under the intake manifold. They would be very expensive to replace. Give me some advice.

Asked by for the 2004 GMC Sierra 1500
It allows the engine to run with the ignition timing as far advanced as possible. The computer will continue to advance the timing until the knock sensor detects pinging. At that point the computer retards the ignition timing just enough for the pinging to stop.

A knock sensor assures that you're getting as much power and fuel economy as is possible from your engine. As long as no unusual "knocking" or "pinging" in cylinder, the sensors will go bad at some point. You may want to replace both sensors at the same point since a bit of labor to replace.

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Upgrades can be made IF you decide to fix this, check for GM TSB. Note: ALWAYS use new manifold bolts!
Or insist on having them installed! Better gaskets and a trick or two for the sensors.