circlerops Posted April 2, 2009 Report Share Posted April 2, 2009 I have a 1998 Cadillac Deville with a Northstar engine. The cooling fans will not turn on when the engine reaches temp. They do come on with the A/C. The engine doesnt over heat going down the road but if left idle it will boil over and the fans do not come on. Is there anyone that can tell me what to look for like a relay or sending unit? I have checked to make sure the fans are plugged in but that is as far as I have gone. Recently I have changed the water pump, the alternator, and the starter is there anything I might have unplugged while doing these things that might keep the fans from coming on? Please help this is wifes car and she is getting very impatient with all the problems we have had with it lately. Link to comment Share on other sites More sharing options...
Bruce Nunnally Posted April 2, 2009 Report Share Posted April 2, 2009 Here is the circuit for the fans: So you probably need to trace the wiring and check the relays. Bruce 2023 Cadillac CT4-V Blackwing Follow me on: Twitter Instagram Youtube Link to comment Share on other sites More sharing options...
joeb Posted April 2, 2009 Report Share Posted April 2, 2009 would leaving the a/c on prevent overheating as a stop-gap measure? that won't fix your issue of the fans not turning on during overheat conditions but it might get you rolling at least. i had another car where the temp gauge used to climb during extended idling and i used to turn on the a/c to force the fans on and the temp would always drop. my cooling fans would come on eventually so it was not a big deal. but it was like having a way to manually control the fans. Link to comment Share on other sites More sharing options...
WarrenJ Posted April 2, 2009 Report Share Posted April 2, 2009 As Bruce's wiring drawing makes clear, the fans are ignited by the PCM (Powertrain Control Module). The fact that A/C operation commands the fans ON verifies the fan wiring, relays, and PCM output are all good. That leaves in question the INPUTS to the PCM that would normally tell it the fans need to be turned on (the PCM, itself, is rarely a point of failure). Step one would be to check the wiring connection at the temperature sending unit; step two would be to check the sending unit itself. Of course, there's more . . . joeb's suggestion about leaving the A/C on to force fan operation seems prudent in the meantime. Regards, Warren There is no means of avoiding the final collapse of a boom brought about by credit expansion. The alternative is only whether the crisis should come sooner as the result of a voluntary abandonment of further credit expansion, or later as a final and total catastrophe of the currency system involved. - Ludwig von Mises Link to comment Share on other sites More sharing options...
circlerops Posted April 2, 2009 Author Report Share Posted April 2, 2009 Warren, I checked the wires going to the sending unit described in your diagram, they look good and they are plugged in properly. I'm going to change the sending unit and see if that helps. If not what else could it be? As Bruce's wiring drawing makes clear, the fans are ignited by the PCM (Powertrain Control Module). The fact that A/C operation commands the fans ON verifies the fan wiring, relays, and PCM output are all good. That leaves in question the INPUTS to the PCM that would normally tell it the fans need to be turned on (the PCM, itself, is rarely a point of failure). Step one would be to check the wiring connection at the temperature sending unit; step two would be to check the sending unit itself. Of course, there's more . . . joeb's suggestion about leaving the A/C on to force fan operation seems prudent in the meantime. Regards, Warren Link to comment Share on other sites More sharing options...
circlerops Posted April 3, 2009 Author Report Share Posted April 3, 2009 The wiring to the sending unit and the unit itself are working properly. Any ideas what else to look for???? Link to comment Share on other sites More sharing options...
Ranger Posted April 3, 2009 Report Share Posted April 3, 2009 would leaving the a/c on prevent overheating as a stop-gap measure? Not likely. Is there anyone that can tell me what to look for Have you tested the coolant for exhaust gases? Link to comment Share on other sites More sharing options...
KHE Posted April 3, 2009 Report Share Posted April 3, 2009 Unplug the coolant temp. sensor and check the resistance of the sensor. At 40 degrees F, the resistance should be around 7280 ohms. The table below shows the approximate resistance of the sensor at a given coolant temperature. 41F = 7280 ohms 50F = 5670 ohms 59F = 4450 ohms 68F = 3520 ohms 77F = 2796 ohms 86F = 2238 ohms 95F = 1802 ohms 104F = 1459 ohms 113F = 1188 ohms 122F = 973 ohms 140F = 667 ohms 158F = 467 ohms 176F = 332 ohms 194F = 241 ohms 212F = 177 ohms If the car sits overnight, the coolant temperature will be the ambient air temperature. When the car is up to operating temperature, the resistance will be approaching the 177 ohm value. Basically, if you monitor the resistance of the sensor, as the engine heats up, the resistance will go down. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
danny117 Posted November 2, 2016 Report Share Posted November 2, 2016 It would appear the fans in the circuit are labeled mechanic view. Clue is alternator and starter replaced. Right side fan not running will kill alternator in a few days with lots of idling. actually alternator shuts down when hot. Relay one is bad because it's the low speed fan that provides constant cooling for alternator and starter when car is idling. Trouble shooting fans at your own risk Testing turn off engine let cool several hours. Check fans work they come out easy. If they don't work replace. turn ignition to koeo pull to ground green wire on fan relay. It should click and both fans run. If it doesn't click or fans don't run replace relay one. Keeping the dark green wire pulled low do the same with the dark blue wire both fans run fast. If this doesn't work replace relay two and three. Still broken Maybe computer failed or its sensor but there would be a code for sensor. Link to comment Share on other sites More sharing options...
rockfangd Posted November 3, 2016 Report Share Posted November 3, 2016 Likely you have a issue related to the relays. They are located at the bottom of the radiator between the engine and the radiator. Also make sure your fans are plugged in, I always have to unplug the passenger side one when replacing the alternator. Welcome to Caddyinfo GM FAN FOREVER Nice, clean, luxury= fine automobile Link to comment Share on other sites More sharing options...
winterset Posted November 4, 2016 Report Share Posted November 4, 2016 I believe one fan comes on when the ac is running, and the other is for cooling the radiator when the car gets near an overheat condition. I have never heard my 2nd fan come on in the 20 years I owned my '96. My dash temp reads from196 to 220 depending on the season, speed, etc. sometimes it will be 220, and it will drop down 20 degrees while driving just a short bit. This does not happen because any fan turns on. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.