1996 Pontiac Sunfire coolant fan not cycling on it's own

I have replaced the coolant temperature sensor, relay, and fuses. The fan is not responding to the temperature sensor. The fan will work when defrost or a/c is engaged. Vehicle has no coolant leaks. Just replaced the water pump and pressure test shows no sign of issues. Mitchell points to new pcm. Anything else I can try before I resort to buying a pre-flashed computer??