01 Tahoe whistling

[rockola1971]

wouldnt a vacum leak show up when spraying ether? also how would i find out if its a clogged cat. these trucks have 2 right?

Usually they just hit it with an Infrared thermometer at the inlet, middle and outlet. The temps should be near one another. A bad one will be substanially cooler on the tail side vs the inlet (toward engine). Harbor freight has the IR thermometers cheap. Usually (bot not always) the downstream oxygen sensors catch a bad cat. Thats the whole purpose of the downstream oxygen sensors. The code is for the downstream(s) being out of range or something along those lines. They have nothing to do with providing information to the PCM for fuel injection adjustments, thats the job of the upstreams (forward of the cats).