the wife's 03 trailblazer(52,000) set a PO495 code and set the SES. My predator came back with an unknown code. Also(not sure if it's related) but the cooling fan doesn't disengage like it's supposed to. It has the semi acceleration sound(or even or Allison tranny sound when cold) ie, the loud whirrrrr until about 50+ mph. I checked the fuses to no avail, and I'm not sure if these two are even related. The fan does spin somewhat easy. However, I can't drive down the road with the hood open to see if the fan is still spinning.

Possibly a bad sensor keeping the fan engaged all the time?

Thanks in advance for any pointers.

P0495 cooling fan speed. Pcm commanding 0 fan speed high. Basically your clutch is bad. There was a reprogram for early S trucks. It may apply to yours as well. Although the clutch is probably the problem.

you need to replace viscous fan clutch and have deale reprogram pcm. have fun changing it flat rate time is about 4hrs.