I have an older 3.8L series II, should be similar. First, I'd locate the relay for the fan(s). Usually can find in the back of the owner's manual. Mine is under the hood, passenger side.
There should be a few like relays which makes swapping easy while troubleshooting, just make sure you know what they do.
Your coolant temp sensor (in intake manifold) should send the voltage to activate the relay, and thereby activating the fan. If the voltage isn't there when hot - it's the coolant sensor, or corrosion on the sensor leads. If it is there and the relay doesn't activate - it's the relay. If it is passed to the fan - it's your fan.
Can't remember if the coolant sensor throws a code or not.