OBD II trouble code P0117 ECT Sensor Circuit Low Voltage is telling you that your 4.0L equipped Ford vehicle's fuel injection computer is seeing a continuous engine coolant temperature of 250°F (121°C) or higher.
The two most common causes of a P0117 trouble code is either a bad ECT sensor or a short in the sensor's wires. In this tutorial, I'm gonna' help you troubleshoot this diagnostic trouble code (DTC) in a step-by-step way.
If a trouble code P0118 is stored in your Ford's PCM's memory, the following tutorial will help:
Here are the contents of this tutorial at a glance:
Since the fuel injection computer needs to know the engine's temperature, via the engine coolant temp (ECT) sensor, when it sees the wrong temperature... your Ford is gonna' have a hard time playing ball.
You may see one or more of the following symptoms when the engine coolant temperature (ECT) sensor fails:
Let's find out what are the common causes of a P0117 DTC, in the next subheading.
In a nutshell, when a code P0117 ECT Sensor Circuit Low Voltage lights up the check engine light (CEL), the PCM is letting you know that it sees a continuous engine coolant temperature of 250°F (121°C) or hotter.
To give you more specifics... the PCM sees this extremely hot temperature as soon as you start your Ford (whose engine is cold) and thru' out the entire time you're driving. The PCM sees this hot temp not because the engine is really overheating, but due to a problem with the sensor or its circuits.
Why is the engine coolant temperature so important for the fuel injection computer? This is due the fact that the colder the engine is, the more fuel the fuel injection computer (known as the PCM = Powertrain Control Module) needs to inject. The warmer the engine is, the less fuel the PCM is needs to inject.
So when the PCM gets the wrong engine coolant temperature... it can no longer control fuel injection to maximize performance and decrease emissions.
Knowing the basics of the engine coolant temperature (ECT) sensor will help diagnose the P0117 ECT Sensor Circuit Low Voltage trouble code lighting up the check engine light.
Briefly, this is how the engine coolant temperature (ECT) sensor works:
|50° F (10° C)||58.75 Ω||3.51 V DC|
|68° F (20° C)||37.30 Ω||3.07 V DC|
|86° F (30° C)||24.27 Ω||2.60 V DC|
|104° F (40° C)||16.15 Ω||2.13 V DC|
|122° F (50° C)||10.97 Ω||1.7 V DC|
|140° F (60° C)||7.70 Ω||1.33 V DC|
|158° F (70° C)||5.37 Ω||1.02 V DC|
|176° F (80° C)||3.84 Ω||0.78 V DC|
|194° F (90° C)||2.80 Ω||0.60 V DC|
|212° F (100° C)||2.07 Ω||0.46 V DC|
The 2 most common cause of trouble code P0117 are:
Although extremely rare for this to happen... a bad PCM can also cause a false P0117 trouble code.
In this tutorial, I'll help you troubleshoot all three of the above. With this basic info under our belts, let's turn the page and get testing!.....
“A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools.”