Auto Electronics: Radiator fan does not work, jeep grand cherokee laredo, jeep grand cherokee

Question
1999 jeep grand cherokee laredo 4.0 engine
I can run the AC while idling until the engine gets
hot and the radiator fan blower will not come on.
I have replaced the relay under the passenger headlamp.
The connector goes directly to the radiator fan.
If I jumper the two large wires on the relay connector
the fan will run. I assume it is an electronic relay.
Can I test it ? What engine sensor operates the relay.
Can you send me the circuit that energizes the relay.
What Is the next most likely cause?
thank you
jim

Answer
Jim, the relay is controlled by the PCM, powertrain control module. If you jumper the Dark Blue/Pink wire at the PCM pin 17, the relay should provide power to the fan. If doing that kicks the fan on, you have a problem with the PCM. A problem with the PCM could mean many things, including no communication on the network, incorrect or skewed input signals and or improper grounds and input power. At that point a scan of the system is in order, preferably with the factory, DRB3, scan tool. This is a complex system that involves the body control module and depending on the system, possibly the electronic temperature controls. Good luck. Don.