Check the fan relays. You can bench test them by applying 12 volts across the coil prongs. You should hear a click, meaning the coil has engaged and switched the element. If no click is heard, I'd check into replacing the defective relays. Also, make sure the radiator is not externally blocked. Make sure that the fins are properly aligned and are not plugged with debris.

On a side note, the general fan circuit is simple to understand. The PCM recieves information from the CTS and based on the resistance reading, it decides whether or not to ground the coil side of the specified relays. Once the PCM grounds the relays, either the high or low fan circuit will be on. A great way to test for fan system functionality is to turn the engine on and turn the A/C on. The cooling fan should be forced on by the PCM. Without air blowing past the condenser, high side pressure would build and render the A/C ineffective. So be sure there's ANY fan activity even with the A/C engaged. If there's no activity, there's either a relay problem, sensor problem, a wiring problem, or a PCM problem.

Ah, and one more thing regarding a pressure test: this is the surefire way to detect a leak. A pressurized system should hold for at least 5 minutes. Without pressure, you don't have an elevated boiling point.

 

Hey man. We have been on vacation dor the last week. Give me or have the wife give my wife a call and we can get together, bring the car and I will throw it on the machine and see what we come up with. Later.

 

Disconnect the plug from the Engine Coolant Temp sensor & and connect the yellow and black wires coming from the PCM together. This will indicate a high coolant temp to the PCM, and the PCM will turn the fan ON. If it does not go on, check the fan relay & wiring, also make sure the black wire from the fan motor has a good clean ground. If you are taking the car in for repair, have them check for combustion gases in the coolant, just in case there is a bad head gasket. Power for the fan motor comes from a fusible link, through the fan relay. Power for the fan relay coil comes from the ignition switch, then through fuse #6 ( 10 AMP)