This article will help you to troubleshoot the engine coolant temperature (ECT) sensor on your GM 4.3L, 5.0L, or 5.7L equipped pick up, van, mini-van or SUV.
You can either use a multimeter or a scan tool (w/ Live Data capability) to diagnose the ECT sensor and/or trouble codes.
Here are the main points of this article:
TIP1: A BAD engine coolant temperature sensor will not cause your pick up (van, mini-van, or SUV) to overheat. This article does not cover any type of overheating issue.
If your vehicle is overheating, I suggest taking a look at these two tests:
TIP2: You'll need a scan tool with Live Data capability to be able to follow the test steps in this article (although you can resistance test the ECT sensor with a multimeter).
You don't need a professional $5K (US) scan tool to do it... a simple generic scan tool will do (Don't have a scan tool? Need a scan tool? Check out my recommendation: Actron CP9580 Scan Tool).
TIP3: Some of my testing suggestions involve tests with the engine running, this means you've got to be on your toes and alert. Think safety all of the time.
The are several symptoms a BAD ECT sensor causes, and they are:
When there's a problem with the ECT sensor or its circuits, the PCM will see one of the three distinct conditions:
You've probably seen the official OBD-II description of these two diagnostic trouble codes... but in plain English what are these two codes saying? Well, this section will shed some light on this (by the way, you're gonna' see the term voltage drop and I'll explain this term in the next section):
P0117: engine coolant temperature (ECT) Circuit Low Input.
P0118: Engine Coolant Temperature (ECT) Circuit High Input
Using a scan tool with Live Data capability is the fastest and easiest way to diagnose an ECT sensor... but sometimes, you've got to verify the sensor's output directly at the sensor... this section will shed some light on how the ECT sensor works so that, if you have to, you can test it directly with a multimeter.
The coolant temperature sensor's resistance changes with temperature (this type of sensor is called a thermistor).
Here are more specifics:
The engine coolant (ECT) temperature sensor has two wires in the connector.
When the coolant is cold (or ambient temperature), the sensor's internal resistance is higher.
As the engine warms up... the coolant starts to heat up, which in turn causes the coolant temp sensor's resistance to decrease.
The following table will help you to see this temperature to resistance relationship:
|50° F (10° C)||5670 Ω|
|68° F (20° C)||3520 Ω|
|86° F (30° C)||2238 Ω|
|104° F (40° C)||1459 Ω|
|122° F (50° C)||973 Ω|
|140° F (60° C)||667 Ω|
|158° F (70° C)||467 Ω|
|176° F (80° C)||332 Ω|
|194° F (90° C)||241 Ω|
|212° F (100° C)||177 Ω|
OK, enough of the working theory...let's get testing in the next page.
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The Hitchhiker's Guide to the Galaxy