Which sensor triggers ECM to turn Elec. Fan on?

[TX MACH 1]

Engine Coolant Temperature Sensor (on lower intake on drivers side close to front)
Engine Coolant Temperature Sender (by oil filler neck/alt. on the heater/coolant lines)

 

[urban96]

i think #2

 

[CManT1914]

Engine Coolant Temperature Sensor (on lower intake on drivers side close to front)
Engine Coolant Temperature Sender (by oil filler neck/alt. on the heater/coolant lines)

You got them backwards. The sending unit is the one actually threaded into the driver's side lower plenum. It controls the temp gauge inside the car. The sensor, located on the end of one of the heater core lines controls everything else, from cold engine fuel enrichment, to turning on/off of fans. The CCRM also controls the fans power supply.

 

[TX MACH 1]

yeah your right, double checked Ford's Tech manual for the description/location.

Does the one on the heater lines crap out alot or is it the other one thats for the gauge on the dash?

 

[CManT1914]

yeah your right, double checked Ford's Tech manual for the description/location.

Does the one on the heater lines crap out alot or is it the other one thats for the gauge on the dash?

The ECT (engine coolant temperature) sensor is the one that goes out fairly commonly. This can cause a whole mess of problems, like fans not working, running rich (air/fuel ratio is also effected by engine temps) and it's generally a good idea to replace it if it's fairly old.

 

[HISSIN50]

Chris has you steered straight.

You can ohm out the ECT (the one for the computer - it is on the pass side) at various temps to see how it is reading. WHen they get off, they can be WAY off.

Good luck.