The PCM- engine computer , energizes the relay ! Is the PCM turning it on ? You could test it with a volt meter or a test light . Does it come on when you turn on the A/C ? If you pull the relay out of the place it plugs into an look on the bottom you should see 4 set's of numbers . 30 & 87 . one of these will have B+ voltage an the other goes to fan . If you jumped this two the fan would run . Now the other numbers 85 & 86 are the control side . One will have B+ voltage the other goes to the PCM . The PCM side one can be tested by hooking up test light to positive voltage an touching the point of test light to 85 or 86 ,which ever doesn't B+ voltage . start the vehicle ,turn on A/C if everything is all right on the control side the test light will lite . The PCM should turn on the fan when engine temp. reaches 212 degrees . You could test that with a up scale scan tool .
Pull the plug off the temperature sensor. This throws the PCM in default mode. The fans should come on at high mode. If not look to wiring, fuses, relays and the PCM. Scanner helps a lot.
SOURCE: Radiator fan will not run but motor is good
On the drivers side in front of the battery there's a black box i think it says fuse turn counter clockwise the black star looking thing on top of the box when it is loose remove cover there should be two relays one is for the fan and other for ac the inside of cover should identify everything fuses etc. You could try turning on AC that should turn on radiator fan.
SOURCE: radiator cooling fan 30 amp. fuse keep blowing
The fan may run with jumper wires but if it''s blowing the 30 Amp Maxifuse it's needs a new or used fan motor.It's pulling too many amps.I have almost never seen a fan relay concern.Only other thing you may check is the wiring down near the fan shoud I have seen the 2 wires get loose from the conduit & melt onto exhaust manifold.Hope tHis Helps
SOURCE: changed radiator fan relay but fan still doesn't
What year is the vehicle? Your coolant temperature sensor may be bad which indicates the system when to turn the electric fan on and off with engine temperature and also a a/c clutch switch that turns the fan on with a/c usage. If the temperature sensor is not operating properly your fan will not come on. Depending on the year, you may have TWO sensors; one is for gauge operation and the other for the PCM and the fan, also known as the ECT (engine coolant temp). It should be a fairly cheap part.
Good luck!
SOURCE: I have a 1999 Jeep Grand Cherokee Laredo 4.0 L 6
TEMP SENSOR IS BAD IT HAS 2 ONE FOR THE GUADGE AND ONE FOR THE FAN
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Sensor is on the exhaust rite next to it right
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