If anyone can help me. I have a 97 z28 and it is sending a code of 1642. I had the car at a shop and was told to reflash the pcm. They said the fans are working fine and the wiring harness is ok, but no signal is coming to the fans untill the high speed fans are signaled on which is at about 220*. I bought a used pcm and had it flashed and installed it and the same code comes up when the car hits obout 210*. I hope someone has some usefull info because the chevy dealer here is useless.

 

I did a search and think I know what to look at.