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Over heating on 84 Corvette

The cooling fan wont come start on my 84 vette. The relay is new and so is the fan swicth. If I ground the wire from the swicth the fan comes on. Do you think I may need a new ECM?

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I realize this is an old post, I am posting mostly for the benefit of others with a similar problem. You DO NOT need a new ECM, it is completely ruled out since it is not included at all in the cooling fan circuit on an 84 Corvette. The circuit includes a temperature switch on the right side of the engine in front of the no. 8 cylinder, it should be a brown wire. This switch grounds at a preset temperature, usually 185-220 degrees depending on model. The temperature switch controls a relay that completes the circuit of positive power to the fan. The fan relay is located on the back of the left wheel well inside the engine compartment. If you have air conditioning, you will also have a pressure switch on the ac that turns the cooling fan on when the ac is on. The fan relay is the weakest link in the cooling fan circuit and is always my first suspect, followed by the temperature switch. The fan can be tested by jumping positive power from the battery. If those test good, start checking continuity on the circuit to rule out an open in the wires. A multi-tester with an ohmmeter will be your friend here. There is also a temperature sensor on the left side of the engine block, this sensor ONLY goes to the digital dash temperature display to alert the driver to the coolant temperature. It does NOT control the fan. There is an air temperature sensor on the intake at the top front middle of the engine that the ECM uses to help control air/fuel mixture, this has nothing to do with the cooling fan at all. Be sure you replaced the right temperature sensor/switch.

Posted on Feb 22, 2012

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Is it overheating before the fans turn on? I beleive the fan turn on point for those cars is 226*. Have you burped the cooling system? An air pocket in the right spot could cause this problem. If the system is burped the problem lies in the fan switch

By grounding the wire to the fan switch your fooling the computer into thinking the engine is at the temperature the switch is supposed to turn the fans on. So it seems that the ecm and the associated wiring is good. When you installed the fan switch into the head did you use any sort of sealant or teflon tape that would stop the switch from getting a good ground? If so, remove the switch and clean off the threads, put a VERY small amount of silicone on the threads and reinstall. Also, verify the connector to the fan switch is clean and making a good connection.

If everything above checks out it is possible you got another bad fan switch.

Posted on Apr 15, 2009

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A good 90 percent of the time the problem is either the ECT sensor, the fan is burnt out or the relays are bad (in that order). It is seldom a computer problem but a computer problem should not be ruled out.

I would check the ECT before replacing the ECM.

Posted on Apr 15, 2009

  • Michael Masters
    Michael Masters Apr 15, 2009

    check the relays as well.

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