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I can only tell you how my 2001 is setup. It's probably the same for you but no guarentees. The radiator fan relay should have 12 volts from pin 1 to ground at all times. You should have 12 volts from pin 2 to ground when the relay is activated. Pin 4 is the 12 volts from the PCM to the coil of the relay, only present when the PCM says the fan should run(***). Pin 3 is the ground for the coil of the relay.
To check: If you know the fan should be running, connect a voltmeter from pin 4 to a good chassis ground. You should read 12 volts. If you don't then the PCM is not telling the relay to start the fans.
If you have 12 volts, then: connect the voltmeter to pin 4 and pin3. If you read 0 volts then you have a ground problem. If you have 12 volts then the coil is good. If the coil is good, and if you have 12 volts to ground from pin 1 of the relay, then measure voltage from pin 2 of the relay to ground. If you have 12 volts, then you have a bad fan motor(s) or the wiring from the relay to the motor(s) is bad. If you have 0 volts from pin 2 to ground then the relay is bad.
***If you never get 12 volts from the PCM then you probably have a bad heat sensor or wiring from a sensor. Remember: "Grounds are important for all components and often the problem".
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