Ford F150 Forum - Community of Ford Truck Fans - EGR, EVAP, PCV, ECT, 02's, TPS, IAT

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Once all the parts are clean, make sure to clean off the Valve Cover opening for the gromment and replace it.
I used a little bit of sealant around the grommet and PCV Valve to help, mainly bevause these should be replaced whenever you do a change. Along with the hoses connecting them to the throttle body housing.
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4) Engine Coolant Temperature (ECT) sensor

How it works.

Your ECT sensor simply works on resistance and sends that to the PCM then to your gauge. The sensor uses a thermistor which is more accurate at smaller intervals than other types of simple resistance based temperature gauges.

A thermistor is a type of resistor whose resistance varies significantly with temperature, more so than in standard resistors. The word is a portmanteau of thermal and resistor. Thermistors are widely used as inrush current limiters, temperature sensors, self-resetting overcurrent protectors, and self-regulating heating elements.

Thermistors differ from resistance temperature detectors (RTD) in that the material used in a thermistor is generally a ceramic or polymer, while RTDs use pure metals. The temperature response is also different; RTDs are useful over larger temperature ranges, while thermistors typically achieve a higher precision within a limited temperature range, typically −90 °C to 130 °C.
http://en.wikipedia.org/wiki/Thermistor
Where is your ECT located?

On my 2003 5.4L it is located on the front of the engine on the drivers side. See picture below for reference.
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How can I check it?
First you need to check two things:
1) That your Sensor is working properly, we will use a resistance test for this
2) Check that the plug to the ECT Sensor has voltage.

Checking for a good ECT sensor and plug.
1) To see that the sensor is working proper unplug the connector, it should only have two terminals on it. (This is with the enginge off). Now with the connector off, prob the terminals of the sensor. Place the positive lead on the right hand side and negative lead on the left as show below.
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Your resistance reading in OHMs should be 60,000 - 40,000 ohms at around 50 degrees Fahrenheit. If it is colder outside your resistance will be higher, so dont worry, that is the way this system works.

Now with everything out of the way let the truck idle until it gets to operating temperate. One it gets to operating temperate re-do step (1) and prob the terminals to check resistance again. Your resistance readings should be between 4,000 and 1,700 ohms from 180-220 degrees F. So it is obvious that resistance increases the colder the engine is, but resistance decreases with an increase in temperature.

It is around 55 degrees here now so I was expecting a resistance reading of around 30,000-40,000 ohms.
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So I can see that my sensor is working properly.

Below is a general physics depiction of the process a guide that can be use to approximate. (This can depend on elevation and of course your model) This is just a general idea, so as long as the resistance is changing adequately, you should be fine.
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2) Now all we need to do is prob the connector to make sure that it is getting ~5.0 volts. Simply use your DMM to prob the connector and see what you get. The dark green wire should read +5.0 volts.

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