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Using Powertrain Computer Scan Tools


You have a new scan tool, so here is how to get the most from it.
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If you have a computer and a scan tool with the ability to store and then transfer the data to a computer, you will have an added advantage. Scan your vehicle when it is in good condition and running perfectly and you can store that data in your computer. You now have a baseline reading that you can use to compare to a later scan when you are having a problem. By checking the "bad" scan with the "good" scan, you will be able to see which system or sensors are "off" and quickly isolate a problem. I have a database of all my regular customers so when they come in with a problem, I know what is "normal" for that particular vehicle.

The hardest problems to locate are intermittent. They can come and go so quickly that the computer doesn't set a DTC. In this case you can do what I do, put the scan tool in Freeze Frame Mode and drive the vehicle. For this you will need an assistant so you can focus on operating the vehicle safely and the assistant can watch the scan tool and activate the freeze frame. When the problem manifests itself, have your assistant press the freeze frame button. This will capture readings from 15 seconds before activation to 15 seconds after. This will allow you to see which sensor is causing the problem.

If you know your vehicle's normal operating condition you can determine if there are deviations, however briefly they occur, that are causing the problem. When you can do this, you will be able to find a bad connection and pinpoint a weak sensor. Now when you replace a part, you will know for sure it was bad.

Using Scan Data For Diagnosis

You will have to learn how to use scan data for diagnosis, and as you use the scan tool you will learn more about reading this data. For instance, a Throttle Position Sensor (TPS) is measured in volts and usually starts at less than one volt, almost at zero, and goes to almost 5 volts at full throttle. As you step on the gas pedal, the reading should show a gradual increase. Some scan tools will show this as an angle. So if the throttle is ½ open, it will read as 50%.

Another example is a Coolant Temperature Sensor (CTS). A CTS is measured in ohms but in a data stream as an actual temperature reading in Fahrenheit or Celsius depending on the scan tools setup.

Here are just some of the things you can check with your scan tool:

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Additional Information provided courtesy of
ALLDATAdiy.com and Warranty Direct
© 2000-2007 Vincent T. Ciulla

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