Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
no problem, this is a pretty simple circuit. the ect wont have any voltages on it. it is only a resistor that sends info to the power control module for engine temp. the cooling fan works like this.
The PCM controls the cooling fan by grounding the cooling fan control circuit which turns ON the cooling fan relay.
The cooling fan relay will be commanded ON when the following conditions are met:
the most common problem is just the coolant fan relay goes bad. the relay has two power feeds, both from the same 30 amp fuse you checked. then the pcm will ground dark green wire to the relay, then the relay sends power to the lt blue wire for the fan motor.
as long both of the part numbers are the same on the relays, this was a very good test. nice job. this means the relay is good. so you are down to either a wiring issue or a pcm problem. most of the time it turns out to be a wiring issues. not too many pcm failures. using the wiring diagram i posted, you wil need to check the wires making sure none of them are broken or shorted or open
the pcm is mounted in behind the right inner fender well down by the rad. look for the dark green wire being broke somewhere between the pcm and relay. you can unplug the pcm and check the green wire, which is connector 2 pin number 54, if you gound this wire with the key on, you should feel the relay click and the fan should come on. i have seen this green wire break around where the harness runs below the rad.