Cooling fan issues

[20mustang16]

I have a 96 GT convertible and I'm having some radiator fan problem. I have replaced constant control module, both sensors on the intake, and replaced thermostat. The problem I'm having is the fan will not kick on unless I unplug the cooling sensor on top of the intake next to the thermostat. With the sensor plugged in the fan will not come on. I cannot figure this out. Anybody have an idea?

 

[wmburns]

First. Have you CONFIRMED that the cooling fan works on BOTH low and high speed? A good method is to run the fan directly from battery with a jumper. There should be an obvious speed difference between the LS and HS. There are three wires. Black goes to ground. Powering either of the other two wires will select the fan to run at LS or HS.

Does the fan come on when the AC is turned on? If not, then the odds favor that the low speed part of the fan is not working.

Want an easier way to test. Then get an ODB2 scanner with bi-directional capability. Using the ODB2 scanner you can command the high speed and low speed fan to turn on. This makes trouble shooting sooooooo much easier.

Here's some information on an affordable Windows based ODB2 solution.

ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/

 

[20mustang16]

The fan does come on when you turn the A/C on

 

[20mustang16]

First. Have you CONFIRMED that the cooling fan works on BOTH low and high speed? A good method is to run the fan directly from battery with a jumper. There should be an obvious speed difference between the LS and HS. There are three wires. Black goes to ground. Powering either of the other two wires will select the fan to run at LS or HS.

Does the fan come on when the AC is turned on? If not, then the odds favor that the low speed part of the fan is not working.

Want an easier way to test. Then get an ODB2 scanner with bi-directional capability. Using the ODB2 scanner you can command the high speed and low speed fan to turn on. This makes trouble shooting sooooooo much easier.

Here's some information on an affordable Windows based ODB2 solution.

ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/

the fan does come on when the a/c is turned on

 

[20mustang16]

both hs and ls does work

 

[wmburns]

If both speed fans do work and the low speed fans works when the AC is turned on plus the fan comes on when the temperature sensor is disconnected that tells us the cooling system is basically working. Something is keeping the PCM from calling for cooling. IF looking for an educated guess, there's something wrong with the sending unit itself. Common reasons include (but not limited to):

• incorrect part used for the application. There is a difference between the dash sensor and the PCM sensor. The sensors are NOT compatible to each other.
• The sensor is in contact with air instead of water. This will make the sensor read low.
• Incorrect system voltage.

IMO the easiest way to trouble shoot this is to "ask" the PCM what it "thinks" the engine coolant temperature is. For this you will need an ODB2 sensor capable of monitoring operational PID's. Here's some information on an affordable Windows based unit.

ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/

Another way to trouble shoot is to compare the expected resistance values with known temperatures. This is documented in the Ford Service manual under the pinpoint tests. If interested in getting a copy for yourself I maybe able to help. PM if interested.