I replaced the temperature control unit, fans still don't come on. When I disconnect the unit within seconds, it comes on (without a jumper).
Got any clues as to what could be wrong? Pretty frustrating.

 

OK, when you say temp control unit do you mean the control head in the dash? When you say fans do you mean fans under hood or fans in dash?

 

I replaced the radiator cooling fans after replacing the radiator itself. It's the "coolant temperature sensor" or sending unit. Brand new and when it's unplugged, the fans work! What's up with that?

 

I think the member is talking about the fan relay for the coolant fan module. What you did with the temp sensor is normal. It may kick the ck engine lite on. If you are looking for the relay, its under the air filter box on the frame rail. If is not what you asking about,let us know.

 

ok, I'm not making myself very clear, sorry about that, been a tiresome day.
The thing I replaced is the temperature sensing unit right next to the thermostat atop the engine. I've not yet replaced the fan relay but when I disconnected or unplugged that new temp sensing unit, the fans came on. The problem now is that I can't figure out how the circuitry works.
Unplugging is like an open circuit yes? The fan shouldn't work, right?
So how is it that the fan goes on after unplugging the darned thing!
Maybe above my expertise and another question, should I bee looking at the fault codes? No engine light is on for now.
I should probably take into the mechanic (not a dealer) to check out the fault codes.

 

The PCM controls the fans based on inputs. Yes, when you unplug the coolant temp sensor the fans will come on. It's a safety default just like if you unplug the Body Control Module the headlamps will come on.

The CTS and fans are not in a series circuit like old school. Everything almost is operated by a module based on a sensor input or a switch request signal. The inputs that the PCM uses to operate fans would be CTS and the AC High Side pressure sensor (transducer, not a switch you can jump across btw) The PCM controls fan speed VIA the solid state relay module.

 

This is an update of sorts: I'm John's wife as he's at work so will try to explain what has happened. Yesterday, we had to go to the doctor, and run a couple of errands in that car. By the time we got to the 2nd stop, the car was overheating, the transmission line leading to rad. came off spewing tranny fluid all over the engine, the belt came off but we did manage to get the car home before too much damage done.
The other problem with the car is that the water pump has been making noises and will need to be changed which he plans to do. He's wondering if water pump inoperative could have created the problem in the 1st place or at least in part, contributed to coolant fans not functioning?
Now we think it might be best to leave fans running all the time by disconnecting coolant temp sensor so engine doesn't overheat, getting car cleaned up & ready for trade in.
The car is in excellent condition body/interior wise and save the rad/fan probs, in decent shape mechanically.
Do y'all think this is our best plan or should we try for getting coolant fans fixed and keeping the car which we would love to do since we just got it paid off and don't want more car pmts.
Me being his wife, you just knew this was going to be a longer than usual post, right?lol.
We surely do appreciate your input more than you can know as this has been quite a mystery to solve concerning the nonfunctioning coolant fans.

 

Hi john and john's wife
Here is what i would do. Replace the water pump,because the blades that rotate on the back of the pump may not be spinning,causing the coolant to boil like a pot of water.2nd i would either replace the thermostat or leave the thermostat out. and 3rd replace the fan relay on the driver side frame rail,which the air filter box would need to be removed.

 

thanks MasterTech, sounds like the plan. I had already replaced the thermostat before I replaced the coolant temp sensor and now will replace the water pump AND the fan relay and remove the thermostat for now. After replacing the fan relay do I need to have the PCM reset? Or is that absolutely necessary?

 

Wouldn't hurt.