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The PCM -engine computer energizes the cooling fan relays , hi an low speed , according to information received from the coolant temp. sensor. an information programmed into the PCM . Usually around 221 degrees the PCM will energize the low speed relay . Is your car's temp . getting that high ? The best way to diagnose these types of problems is by hooking up a scan tool that can read engine sensor data parameters to see what the temp. of the engine is . Also a scan tool with bi-directional controls , this would be useful to see if the PCM can control the fans ! There could be DTC'S - diagnostic trouble codes stored in the PCM . Not all DTC'S turn on the MIL light , check engine etc..
The rad fan is turned on by the computer when the temp reaches a certain heat degree. The computer gets information from the coolant temp sensor in the engine to tell it when to ground the relay. You may have a blown fuse/bad fan/bad relay/power supply to relay/or PCM problem causing the fan to not operate
Try checking the fuse box under the hood. It should have a fuse marked cooling fan or cooling system. If the car does start, that means the computer isn't out, but maybe there is a bad relay by the fan or in the circuit or even the temp sensor may be bad. The fan won't run until the temp is high enough; usually by the time the thermostat opens.
On a vehicle this age, it is likely that the fans themselves have worn out. Test the fans by running battery power directly to the positive contact. If they start, they are OK. On 4.3 motors, there is also a seperate temp sensor to signal the fans, usually called a fan switch. I believe it operates independent of the ECM. Another possible culprit is a bad ground at the fans or even a loose or corroded negative battery cable.
yeah try to change the sensor.maybe it is busted. normally, most of the late-model cars comes with a fan feature that turns of after 5 or 10 mins even after switching off the engine. this helps to cool down first the engine to reach its desirable temperature before it is totally shut down. its good that your radiator fan has a feature like that. aftermarket perfomance fans do come with that feature because it takes care of the engine state.just try to change the sensor for engine temp