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Eric
Eric, Automotive Repair Shop Manager
Category: Ford
Satisfied Customers: 29985
Experience:  Automotive Repair Shop Manager, Technician
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Trying to locate coolant temperature sensor so i can replace

Customer Question

trying to locate coolant temperature sensor so i can replace it
JA: Have you checked the connectors on the sensor itself? It's important that they not be loose or corroded.
Customer: need to find it first
JA: What is the model/year of your Ford?
Customer: 2004 freestar 4.2L
JA: Are you fixing your Freestar yourself? What have you tried so far?
Customer: thermostat
JA: Anything else you want the mechanic to know before I connect you?
Customer: no that it
Submitted: 1 month ago.
Category: Ford
Expert:  Eric replied 1 month ago.

HI,

Ok, your engine does not have an engine coolant temperature (ECT) sensor. It instead uses a cylinder head temperature(CHT) sensor for coolant temperature monitoring for the computer. It is attached at rear of left cylinder head - see attached

This describes the CHT sensor in detail for you

The CHT sensor

^ sends the PCM a signal indicating cylinder head temperature.
^ resistance decreases as coolant temperature increases.

The cylinder head temperature (CHT) sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as temperature increases, and increases as temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.

Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow.

Voltage that is dropped across a fixed resistor in series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.

The cylinder head temperature (CHT) sensor is installed in the aluminum cylinder head and measures the metal temperature. The CHT sensor can provide complete engine temperature information and can be used to infer coolant temperature. If the CHT sensor conveys an overheating condition to the PCM, the PCM would then initiate a fail-safe cooling strategy based on information from the CHT sensor. A cooling system failure such as low coolant or coolant loss could cause an overheating condition. As a result, damage to major engine components could occur. Using both the CHT sensor and fail-safe cooling strategy, the PCM prevents damage by allowing air cooling of the engine and limp home capability.

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Expert:  Eric replied 1 month ago.

I noticed we have not yet resolved your concern you asked about. I would sure appreciate it if you would reply so I can offer my skills and knowledge and repair guide access to help as best I can.

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Expert:  Eric replied 1 month ago.

I noticed we have not yet resolved your concern you asked about. I would sure appreciate it if you would reply so I can offer my skills and knowledge and repair guide access to help as best I can.

~Do you still need more help?
~Confused by my info request or answer?
~Need more time?
~Confused on how the site works?
~Need more detail or a different explanation?

If the answer is YES to any of these just press reply and lets work on this concern some more.

If you have new questions now or in the future please do not hesitate to ask them. If you would like me to assist you. Just bookmark this page so you can access my profile easy and post a new question from the question box on my profile page.

Please remember to rate service using the rating page so that I may receive credit. Thanks

Please note that if you have a subscription service, you still are required to rate service, however you are not charged again. This is just so that your expert is credited for their time and services. Thank you.

Expert:  Eric replied 1 month ago.

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Expert:  Eric replied 30 days ago.

I noticed we have not yet resolved your concern you asked about. I would sure appreciate it if you would reply so I can offer my skills and knowledge and repair guide access to help as best I can.

~Do you still need more help?
~Confused by my info request or answer?
~Need more time?
~Confused on how the site works?
~Need more detail or a different explanation?

If the answer is YES to any of these just press reply and lets work on this concern some more.

If you have new questions now or in the future please do not hesitate to ask them. If you would like me to assist you. Just bookmark this page so you can access my profile easy and post a new question from the question box on my profile page.

Please remember to rate service using the rating page so that I may receive credit. Thanks

Please note that if you have a subscription service, you still are required to rate service, however you are not charged again. This is just so that your expert is credited for their time and services. Thank you.