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Discussion Starter #1
So last night, I was driving to go get my sister from work. It was kinda chilly out.. I live in Florida so what we think is chilly is quite warm to others.

My duratec decides now is a great time to light up the CEL.. first time I've EVER seen that light since I've owned this car. I panic of course and drive it back home because I thought I messed something up.

At first I thought I screwed up my MAF by self washing my car because I sprayed water at the grill of the car before starting it up and driving. I've driven in heavy rain and puddles and my intake has been just fine after all that.. so I ruled that out.

Today I went to get the trouble code read at Advance auto, it shows the Cooling Temperature Sensor was acting up. (I need to invest in a code reader) The reading was below operating temperature apparently. The coolant level is fine and the car hasn't over heated so I'm a bit lost..

I don't quite remember what the OBDII reader said but it was something like that. Still very weird..
 

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was the code P0128 Coolant thermostat (coolant temperature below thermostat regulating temperature)? if it was the thermostat is sticking and needs replaced.
 

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Yeah it's a P0128. I went back and double checked. However some say it's the sensor that's going bad.. I still want to change the thermostat anyways. The car probably still has the original thermostat too.
 

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According to the 2006 Focus FSM DTC P0128 states "The engine does not reach normal operating temperature" and states to check the thermostat.

First I would check to see what temperature the sender thinks the temperature of the engine is, if it is drastically low (below ambient temperature) when the engine is running then then it is probably the cylinder head temperature (CHT) sender in the cylinder head between cylinders 2 and 3 or the wiring for it. To check the wiring check to see if the White/Violet wire for the CHT is above 5 volts and the Brown/White wire should be shorted to (PCM) ground. To check the CHT itself the resistance between the 2 pins on it should be between 965.808 ohms (-40degrees) and 1.155 ohms (248 degrees F) but for ambient temperatures 50-85 degrees F should be between 59.175 and 24.215 ohms, with the reading being higher the colder it is.

If the computer sees engine temp is below 160 degrees but above ambient temperature then the thermostat may be stuck open thereby not allowing the engine to get up to operating temperature.
 
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