2004 Avalanche, 5.3 with 241K miles. My CEL came on two months ago, traced it to a knock sensor. Mechanic replaced the KS and the wiring harness. CEL came back on a few weeks later. This time the other side KS is throwing the CEL. Mechanic went back in, replaced the other KS, and its wiring. Drove it and next day CEL came back on, still indicating KS. Mech reset the CEL. Drove it next day, and CEL comes on again. My mech is baffeled. He does not know what to do next, except reset the CEL. Can anyone offer help? Thanks!