Using an Auto Scan Tool

You’re cruising across the countryside; it’s a gorgeous, illuminating summer afternoon, and your car‘s performance is nearly perfect.
All is right with the world, except that your check engine light has begun to pierce your retinas and paralyze you with fear. Why must this foreboding light torment you so? The car seems to be running as it always has been and doesn’t seem to have a problem idling.

Maybe those mischievous electrons in your car wiring are playing tricks on you. This glow will probably fade soon, right? Eventually it does, but it soon returns, erratically reappearing to torment you further. To keep you ever questioning when the car might explode like a Michael Bay film.

Back at the Beginning

In 1996, the EPA mandated that a new common standard must be met by the computer interface of all vehicles sold in the United States. This eliminated the need for aftermarket repair shops to have to buy dozens of different scan tools that would cost them over $2000; in order to work on as many vehicle brands as possible.

This standard is known as OBD II (On-Board Diagnostics, version II). Computers are required to run the fuel injection, ignition system, and the automated transmission on most modern fuel-injected cars and trucks. Data is collected from these monitor sensors from the engine and other systems throughout the vehicles. The computer sends commands to the fuel injectors and ignition coils in order to fire the cylinders. This data is used to fine-tune the combustion process with the correct amount of gasoline and the correct ignition timing to provide efficient, clean combustion for efficient power, economy, and low pollution. There are many sensors, measuring features such as throttle opening, engine rpm, air and coolant temperature, crankshaft and camshaft position, and road speed.

This is a complicated, high-speed system with many self-checks that are meant to keep your car running for a very long time. Tune ups have started to become virtually obsolete due to this computer system’s ability to self-correct the fuel mixture and ignition at every crankshaft revolution. This is a significant improvement over the past, when public transportation was required to travel to a garage for an annual tune up.

This sounds amazing until something goes wrong. Usually, the first sign of a disturbance in the force is the awakening of the crimson alert that is the check engine light. This light is tagged by the OBD II standard as the MIL (malfunction indicator lamp). This light indicated that the PCM (powertrain control module) is seeing data from some sensor that doesn’t computer.
This data is far enough out of bounds that the PCM can’t perform a decisive action. This leads the PCM to make a guess at what should be a good number to substitute for the sensor’s erratic output and continues functioning in order to get you home safe to your younglings. This light also displays the MIL so you will know that something is wrong. Surprisingly, your vehicle continues to run as if everything is fine. However, you will start to notice a slight loss of power and increased fuel consumption.

That’s not all. The PCM also retains a diagnostic “trouble code” so a service technician can know where to look for the problem. Professional technicians have been relying on scan tools to check these codes for years because they were cheap and dedicated to one manufacturer’s vehicles. For example, a scan tool for a Mercedes wouldn’t work on a Chevy.

Thanks to the march of technological advancement, these scan tools have become cheap enough for car owners to buy. Scan tools can come in the form of a code reader that shows trouble codes for as little as $50 or up, for upgradeable machines with multi-language features and a computer interface.

Break the Code

1. In order to begin this process, plug the scan tool into the OBD II connector located under the dash. Turn the key on, but don’t start the engine.
2. The tool will inquire for various bits of information, such as: the VIN, make and model of the car, and the engine type. Simply follow the onscreen instructions.
3. Eventually, you will arrive at the option to check for trouble codes and other menu options. Certain higher-end scan tools provide a text explanation of the code onscreen. Others include a CD-ROM or a paper pamphlet listing what the codes mean.
   
   

   The internet is your friend; you can use it to find a trouble-code list on any site that focuses on your particular vehicle. There could even be information that may be even more helpful than the code. After reading these codes, write them down before resetting the MIL indicator.

4. The menu also provides an option for Inspection and Maintenance (I/M). Your car needs to be driven until the PCM is convinced that the fault has been corrected, if you have turned off the MIL.

Common Questions

Q. How long must you drive?
A. Different manufacturers have various ideas, however, a few days of normal driving should be sufficient to pass the I/M readiness tests.

Q. Does it REALLY matter?
A. Yes it does, because if you go to the nightmare realm of the DMV or an independent station for an inspection, the technician will most likely use his own scan tool.

If your car fails the I/M readiness test, you won’t pass an emissions test, and will not get a sticker. I/M readiness is vital in order to prevent people from sneaking a poorly running cars through the emissions test by cleaning codes prior to pulling up to the DMV.

Luckily, most cheap code readers (below $200) can provide you with this information and even allow you to clear the codes and turn off the MIL light. Be careful not to mistake a simple code reader for a genuine scan tool, some of them are deceptively labeled as such. Usually a code reader is more than capable of catching most simple problems.

What Does the Scanner See?

Viewing data is another option that is available on the menu of most scanning tools. This feature can usually get you to the source of the problem faster.

This option allows you to screen through the actual numbers that the PCM is reading from the sensors. This allows you to check things like water, air temperature, oxygen-sensor function, engine load and rpm, and a plethora of various potential sources of problems. All of this is provided in real time.

A freeze-frame function that can trap data when something goes wrong during a drive is also a common feature on these devices. The ignition timing and injector pulse width are important bits of data that are usually presented at the first sign of error to your mechanic, or you. This allows you to figure out what went wrong with less difficulty.

Pro-grade scan tools feature graphic functions that allow a technician to view several parameters onscreen while the engine is running. Consumer-grade machines usually do not allow for this. However, some higher-end ones, that cost hundreds of dollars; have an interface that can hook up to a laptop or desktop. This doesn’t mean that you have to lug your processing mechanical beast down to the garage. Scan tools have more than enough memory and battery life to allow you to plug them in with the car cable disconnected.

Some versions of interfaces and software actually allow you to hook up your computer directly to the OBD II connector via USB. This lets you look at the data on the computer screen and make a printout. These features can provide you with a much welcomed advantage but it will cost from $200 up. That same price range can buy you a dedicated scan tool.

Check Out eToolsCity's Selection of  OBD-II Scanners and Automotive Diagnostic Tools!

Launch CREADER VI+ OBD2 Code Reader	Launch CR VII Obdii Diagnostic Scan Tool	Launch Code Reader for Heavy Duty Truck Applications	Launch Creader Professional CRP129 Pro-Code OBDII Scan Diagnostic Tool