I have a 1995 Chrysler Concorde with a 3.5L engine & the cooling fans work when they suppose to but not every time.When they don't come on when needed(temp gauge above halfway)there is no signal from the computer to ground the cooling fan relay(low speed).All the other signals for the relay are there but sometimes the computer don't provide a ground.I replaced the coolant temp sensor.This is a weird problem as the car will operate fine for hours at a time but when the cooling fans don't work when needed,the car overheatsThis problem happens out of the blue & I can't figure out why.I have access to Alldata but it don't include the coolant temp sensor in the wiring diagram for the cooling fansSo I can't tell what info the computer needs to turn on the cooling fans.The a/c belt is missing so turning on the a/c for any checks is not possible.I pulled the high speed fan relay so the fans are on all the time when the key is in run position until I can get more info.What does the computer need info from to activate the cooling fans?Anyone else have this problem?The car also randomly dies for no reason but it restarts evertime afterwards.A used computer was installed awhile ago for unknown reasons.When there is the signal loss from computer,I used apaperclip & bypassed relay & fans came on.Any help would be appricated

 

The computer reads the data from the engine coolant temperatire sensor to decide whether to activate the fans. The system includes the temperature sensor, the computer, the relay, the fan, and, of course, the wiring that connects them. A failure of any one component breaks the chain.

To check the sensor, check its resistance when cold. Then warm it up and check again, it should have less resistance. Its resistance increases as temperature decreases, and vice versa.

The temperature gauge in the car operates off the same sensor, so if that's working properly, the sensor is probably good.

Have you checked the relay? Maybe just replace it as they are fairly cheap.

Check the wiring as best you can.

On a 16 year-old car, lots of things can begin to break down.

 

Unplug the coolant sensor. This will force PCM into default mode.....and turn the fans on....

Trace the "TRIGGER WIRE" back to pCM.....if the wire integrity is good, and you still have no trigger.....Its PCM time.

 

Thanks guys for the replies.The relay is fine,the signal(computer grounds relay)wire drops out sometimes.The temp gauge works properly.It is also new(coolant temp sensor).When I unplug the coolant temp sensor when engine is running,the fans do not come on.What does this meanYou guys think the computer is bad?My other question is if the cooling fan motors get too hot,will the computer shut off the signal wire to the relay?I tapped on computer to see if fans will turn on(when fans are not coming on when needed/coolant temp is high)& nothing happens,I also sprayed computer with cool water to see if that turns fans on but that also does nothingWhat does the little module looking thing do that is at bottom of cooling fans?Its a small rectangle shaped plastic thing.Could that have something to do with my issue?I pulled the high speed relay & the fans come on all the time with key in run position