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Discussion Starter #1
Hey everyone I’m struggling with my Deville trying to overheat. It only does it when it’s under a load. I live in a very mountainous area & when I climb a hill the temperature goes up to the third mark, normally it’s dead center, when I go down the other side it cools back down. The a/c fan comes on but the cooling fan doesn’t. I’ve checked fuses & tested the fan motors everything is good. I should mention that there’s a loss in power also. It barely climbs the hills & mountains but has no problem on a flat road. Help please!!!
 

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White Diamond '03 DHS (with DTS floor shift)
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Welcome

Overheating under a load is a sign of a HG failure in it's early stages. First check that the purge line is clear and flows coolant. If that's OK, then do a block test just to rule out the HG's. so you don't go off chasing your tail.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Welcome to CF !!!

Your car has its own built-in trouble code scanner/memory. Use the correct model/year group of instructions in the sticky thread "How to pull codes". Write them all down, use the embedded OBD-II link to define any found codes and post it all here.

Here's your cooling fan schematic. Check the fuses and relays. Yes, make sure the coolant purge line is clear and flowing a small stream into the surge tank - common cause of the overheats you describe.

Fan control circuit-2000+.gif
 

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Discussion Starter #4
Thanks for the help. I have checked the fuses & relays & direct wired the fans to make sure they are both working. The cooling fan works perfectly with direct power but won’t work when in the car? Could it be the coolant temp sensor not turning the cooling fan on? The AC fan works like it’s supposed to.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Please read the first paragraph in Post #3. The fan circuits and ECT are all monitored for faults - there may be trouble codes set.
 

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2014 ELR
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you say AC fan and cooling fan. Are you referring to both the fans on the radiator?
They are both cooling fans and they should both run either slow or fast, based on the wiring diagram. When the AC is turned on both fans should run on low speed. If the engine gets hot they should both switch to high speed. If you look at what the relays do you will see that the low speed relay applies power to one fan wire. The other wire of that fan runs to the s/p (series parallel) relay where it then connecto to one wire of the second fan. The other wire of the second fan is connected to ground. This way both fans are connected in series and each fan gets half of the battery voltage. This makes them eun slow and quiet. When the coolin fan 2 relay is turned on the s/p relay is also turned on this now applys 12v power to both fans independently, running them fast and much louder. You need to check all three relays and all the grounds. Use the above circuit to check wiring.
Which fan runs? The left or the right (as viewed from the drivers seat)
Is it running slow or fast. On slow speed you almost can't hear it running, on high speed it is quite noisy.
 
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