03 Tahoe NO START!!! CRANK SENSOR VOLTAGE IS WACKED

[03Chevy]

My 03 Tahoe stopped running. replaced everything you could think of..sometimes if crank on it for a long time it wI'll fire..when i tested the crank sensor wires at the PCM it showed 12volts at the green wire ..ground on the black and yellow and and the blue and white it showed 9 or 10volts with the key on and drops to 5 when I crank it over... From studies I came up with the blue and white wire is suppose to show a on/off signal..why does my blue and wwhite constantly have voltage???? PLEASE HELP