don309

Can someone tell me if I have a bad Coolant Temperature Sensor, will that stop the fan from coming on???? PLEASE HELP

PatHenry

If you're talking about the aux fan, it could.

If you disconnect the CTS when the vehicle is running does the fan come on? (It should.)

don309

I am a real novice, on a fixed income trying to DIY. I don't even know what a CTS is. I mean the cooling fan. If I may here's what happened. Over the weekend my radiator blew up. I have a 2004 Grand Cherokee Laredo 4.0l L6. I replaced the radiator, hoses, thermostat. I filled with coolant Ran the heater, squeezed the hoses. Thought the air was out. It runs ok while moving. Got home left it run, gauge went right to 3/4 hot. Is their a bleeder valve?? Any ideas? I am by no way a mechanic!! I'm on a fixed income, so have to try anything first. If there is anyone that can help out, it would be greatly appreciated. Today I noticed the cooling fan doesn't come on.
Don

PatHenry

Is it just one big fan in the front? (I think on the GC 04 it would be)

If it's not moving you have a bad fan clutch. It's not hard to replace with hand tools (you need a pretty big wrench to get it off if it's anything like my 00 TJ), but it's fairly inexpensive to replace and definitely something a novice could handle.

EDIT - Wait - I'm not sure if those are electric or mechanical. If the fan is connected to a pulley on the engine, it's mechanical. If it's like a house fan looking thing then it's electric.

The CTS is the thing on the side of the thermostat housing with the wires connected to it.

Sorry, I'm not super familiar with Grand Cherokees - you might want to check the grand cherokee forum.

www.cherokeeforum.com/f5/

don309

Yes it's electrical. I know what your talking about. I was trying to get the plug off the heat sensor. But the clip is busted, I'll get it off and see if the fan runs. Thank you so much for taking the time!!!

fb97xj1

CTS = Coolant Temperature Sensor.

Jimbo Slice

Stop.

Disconnect the electric fan, take two jumper wires and stuff one each into the fan side of the plug you just disconnected... then touch one to the battery positive and one to the battery negative.

Does the fan spin?

dave1123

The electric fan is switched by 2 relays in the fuse box under the hood. These relays are controlled by the computer reading the temperature sensor at the thermostat and sending commands to the correct relay, one for high and one for low speed. Nothing on these Jeeps is a direct circuit anymore. Everything is controlled by the computer thru a data bus. Old school electricity concepts don't work anymore. The sensors work on a 5 volt supply and all the switching is done by relays. Even the temperature gauge gets it's information from the computer (PCM). For you computer geniuses, they are analog data impulses, not digital. The sensors are simply thermistors (resistors that change value with temperature). The later 2-relay system is far superior to the pulse-modulated fan relay found on the 99-01 WJ. That thing was always burning out!

The 04 should have a 3 wire fan connector. High speed, low speed, and ground. My 2000 has a 2 wire plug and the fan speed is controlled from that stupid pulse-modulated relay found under the right headlight. Also, the fans are permanent magnet motors so polarity is important for fan direction. A fan running in reverse blows air out the front and will cause an overheat going down the highway!

My thought is when the OE system screws up, it's best to install an aftermarket stand-alone control system. Of course, these are MY opinions.