I have a 99 silverado and the check engine light came on and I ran a diagnostic test,these things came up, Knock sensor low input, and the 2 oxygen sensors or the passenger side were bad. So i replaced the two oxygen sensors, and cleared the dtc's, in hope that they would fix my knock sensor problem. I could here the pistons knocking before i replaced the o2 sensors, I've driven about 30 miles and the truck seems to drive better, but the knocking came back so i ran another diagnostic test, and the knock sensor problem has come back up. From my understanding, in order to replace the knock sensors you have to take the intake manifold completely off, am i right? And is that a hard job? If i need to do that i was thinking i probably should replace anything that's in there just because i have the intake manifold off and nothing has been replaced in there, so if anyone knows any information on this stuff it would be very helpful. My truck is a 1500, and has 150k miles on it. Thanks!