Re: Ive Searched Every where..
The fan(s) should come on when DEF or A/C is selected. Fan relay controlled by the ECM.
If dual fans, one is controlled by the heat sensor/switch in the engine block/manifold. It closes at some 225*F-235*F, and fan comes on. The other fan is controlled by ECM getting input from a two-wire coolant sensor. The ECM relay has battery on one side of the coil and the ECM has the return.
When no fan needed, the ECM has a high voltage. Temp satisfied, ECM places a low, 0.5 volts and this action energizes the relay, fan on. Relay has a large gauge wire for fan power to one contact, and the other to the fan motor. Ground is supplied at the fan plug.
Or, for ther engine fan, the engine has a temp switch and ground is through the body threads to engine, closes when temp is reached, 230*F(?), energizes the relay, fan on.
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