PO327 Error Code-Knock Sensor

On my 2001 Tahoe, 5.3, I got a "Service Engine" light and an error code yesterday: "PO327 Knock Sensor 1 Circuit Low Input".

I reset it and it came back after 5 miles.

Could this be about poor fuel (used 87 octane CITGO) or more likely a bad sensor?

I've tried to mix in half a tank of premium but haven't driven far enough to see if raising the average octane to 90 will make a change or not.

Where is it, or are they? Accessible?

You have to remove the intake manifold to access the knock sensors. There are two of them. KS 1 is towards the front of the truck. With that code, I'd lean more towards a bad sensor.