Scan Tool Essentials You Should Know!

Scan Tool Essentials You Should Know!

A scan tool is a great tool to have, since sooner or later, the check engine light will come on in your vehicle (inevitable as death and taxes).

But although a scan tool is now a must-have tool, there are many big misconceptions about what it can and can not do.

In this article, I'll try to dispel some of the most common misconceptions that will help you to see your scan tool in a new light (and be able to make effective use of it).

The Bare Essentials

All modern fuel injected vehicles have computers controlling the injection of fuel and the creation of spark to start and keep the engine running. Not only that, if the vehicle is equipped with an automatic transmission, it will also be controlled by the same computer or a dedicated transmission computer.

Eventually, the input sensors that help these computers make decisions and keep the vehicle running smoothly and from polluting too much will fail and need to be replaced.

When this happens, the very first symptoms you'll see is the check engine light (CEL) lighting up on your instrument cluster. Why? Well, because all modern fuel injected gasoline engine vehicles have On Board Diagnostics (OBD) integrated in their computers.

It's the job of the OBD system to monitor for failures since a failure in any of the input sensors and output devices will mean that your vehicle will pollute more than it should and of course, your vehicle will not run right.

The tool that's used to interface with your vehicle's On Board Diagnostic system is the scan tool. And so, in a nutshell, to diagnose this check engine light and the problem causing the it light up, you'll need a scan tool.

Common Misconceptions

Taking into consideration that the scan tool will help you to diagnose a check engine light problem, you can conclude that the scan tool is a very important tool to own and to know how to use.

But, there are some very serious misconceptions about what the scan tool can do. Two of the most common are:

Misconception #1: The scan tool will tell you exactly what to replace. This myth costs consumers a ton of money every year. How? Because the vehicle owner (and even the professional auto mechanics) assume that if the diagnostic trouble code is accusing so and so part, it must be bad and should be replaced no questions asked. Sadly, this is not true.

In my long experience working on cars (and of course this is just my opinion), a scan tool will only tell you exactly what's wrong about 20% of the time. Now, don't let this frustrate you, I'll explain this issue some more in the next subheading.

Misconception #2: That connecting a scan tool and reading the diagnostic trouble codes is a diagnostic. This myth also leads to a great big money pit.

Check Engine Light Came Back!

The biggest reason why the check engine light comes back (or never goes away) after replacing the parts the code or codes indicated as being bad, is that those parts were not independently verified apart from the scan tool.

No, I don't mean that the part had to be physically removed and taken to the factory dealer or an auto repair shop to get independently tested. What I mean is that after reading the trouble codes, no tests were performed on the said parts to make sure they were truly fried.

Yes, it is possible to make sure that what the scan tool is telling you is fried, and lighting up the check engine light, is really bad. Let's turn the page and find out more about this.

How To Effectively Use A Scan Tool

Owning a scan tool can really pay off for you in the short term and in the long run. And to make this pay off happen, you need to be aware of this: A scan tool is just a tool that needs to be used in conjunction with a few others (like a multimeter, fuel pressure gauge, etc.) and specific testing information. This ‘specific testing information’ may be a repair manual, or an internet site with automotive testing info (like this one).

Let me give you an example that might bring this home: a ratchet wrench is a must-have tool if you plan on replacing your front brake pads. But just the ratchet wrench is not gonna' get the whole job done. You'll need a jack, jack stands, the right sockets (to attach to the ratchet wrench) to remove the caliper bolts, etc.

Does this mean that you're gonna' spend a fortune on tools to do your own brakes? NO. Are you gonna' save money? YES, considering that most repair shops (at least at the ones where I have worked at) charge around $500 to $700 to replace front brake pads and rotors. And if you plan on driving your vehicle, you're gonna' eventually need new brake pads again.

For the scan tool to be an effective money saving tool, you're gonna' need more than a scan tool to effectively troubleshoot the problem lighting up the check engine light.

The Strategy That Will Get The Most Out Of Your Scan Tool

By now, you're probably starting to see that the most effective strategy (to save money and time) is to test the sensor or sensors that your scan tool is telling you are bad. Never take the scan tool at its word that the sensor is bad. Instead, test it to make sure.

You can easily accomplish this by researching the diagnostic trouble codes in a repair manual or on the Internet.

Of course, you're also gonna' need to invest in more tools. There's no way around this and I want to be very frank with you. Without the appropriate tools and the appropriate testing info (such as that found in repair manuals) to test the sensor your scan tool is accusing of being bad, you are always gonna' be groping in the dark. This always results in replacing good parts that don't need to be replaced.

As I mentioned before, you don't have to spend an arm and a leg on these tools. But spend you will have to.

So, if you have already invested in a scan tool, learn more about it either in books or on-line. Troubleshooting check engine light problems don't have to be a nightmare and an exercise in wasting time and money if you remember that reading the diagnostic trouble codes is only the first step of the journey.

What Is Live Data?

Scan tools can be divided into two main types. code readers and code readers with Live Data capability.

Live Data is the capability to display some of the input and output that the PCM in your car sees and sends out.

The benefit of being able to see Live Data are several, here's a basic list:

  • You're able to see the specific signals of the sensor you need or want to test (as long as the scan tool has a PID for the sensor).
  • Since most sensors can be independently tested with a multimeter, being able to compare the signal output (on your multimeter) to what the PCM is seeing will help you in troubleshooting an open-circuit problem or a bad PCM.
  • It'll speed up your diagnostic since you're able to get a quick view of what the sensor is doing or not doing.

Related Articles

The following two are scan tool reviews you might be interested in reading: