90% of the 80e trans have two speedo sensors, one in the tailhousing and one on the input drum. The PCM compares the two to check for clutch slippage and many other things. The PCM outputs the signal to the speedometer using an isolated single wire feed to the speedo. Yes, the PCM controls the on/off of the fans if you install it that way. You can control the on/off temp in the PCM tune.