LS PCM not turning on the fans

[terrydmorgan]

Since the fans come on when you manually ground pin 85 of the relays, you know the fans/relays work if a ground is applied to that pin. Thus, it sounds like the PCM isn't grounding pin 85 on the drivers or the passenger side fans. Have you tried turning on the AC to see if the passenger side fan comes on? At least you'll be able to verify that the AC pressure switch is wired properly, and that will allow you to run one fan. You could wire the drivers side fan pin 85 through a manual toggle switch to ground at least temporarily to allow you to operate the drivers side fan.

In the mean time, disconnect the PCM lines to pin 85 and put a scope on them to see if they are in fact providing any ground when the temperature is high enough. If you don't have a scope, connect a tester between +battery, such as at pin 30, and the blue pin of the PCM (disconnected from the relay). If it lights up, PCM is giving you a ground on that line. On the other hand, if no light, then no ground and that's your problem and you have to figure out why PCM isn't providing a ground. The problem may be the temp sender or the PCM itself. Do you have temp sensor connected to PCM? If so, verify that the temp sender is working properly. For example, are you using PCM to drive temp gauge? If so, and the temp gauge works properly, then the temp sender is working and your problem is likely in the PCM and may need reprogramming.