Automotive Scan Tool and Diagnosis

This is a short article on how to pick out the right automotive scan tool based on needs and why you might want a scanner instead of just a code reader. The difference is, scanners can read the data stream. See what these cost effective tools can and cannot do. Discover how to use it properly to diagnose some of the most common generic codes found set in memory.

At the bottom of this short page is a link to pictures and reviews of scanners I own. I picked the Equus 3040 on the right as a good compromise between cost and features. Also on this page is a discussion about common oxygen sensor codes, diagnosis tips and a video showing how to replace an o2 if it's needed.

Connecting the diagnostic tool to a vehicle, pulling out the codes and then resetting the light is one of your auto repair shops favorite jobs. They don't have to get dirty, bust their knuckles and it pays well. Some charge a flat rate diagnostic fee of 1 hour for this operation. Although, many shops will apply this to any repairs purchased.

Code Reader Type Scan Tools

For as little as $20 you can have your own automotive code reader. Many offer 1 or 2 button operation and aren't that hard to figure out for home use. This means you can perform initial diagnosis when the service engine soon light or check engine light comes on.

I would like to mention that most of the scan tools and code readers today come with an in-depth operation manual and a money back guarantee. This leaves little to worry about in terms of learning curves or waste of working capital. The manuals will explain how to pull and erase codes plus offer information on what it stands for.

As I mentioned in a few previous articles, sometimes codes are intermittent and clearing or erasing them is all that needs to be done to keep the light off for good. If you erase and it immediately comes back or returns in 24 hours of operation this is a hard failure. Here's an example of a hard code.

car code reader

For this example of automotive scan tool operation and reading the comprehensive data I'll give you a very common code that you just might find set in the automobile computer memory some day.

I come across the oxygen sensor voltage low or high code all the time. Many mechanics when they find this code just want to go ahead and replace the oxygen sensors. This may not be the right move.

When you pull this code up on your automotive scan tool, the first thing you want to do is reset it and see if it returns. If the warning lamp comes back on and the code has reset the second thing you do is read the data stream for the oxygen sensors.

Reading scan tool data for this code using the collected information from the cars main computer is easier then many would think. If you have an Actron scanner that can view the data stream you can record the information in snap shot mode or run the specialized O2 monitor test mode.

oxygen sensor operation

o2 sensor cross counts graph

The oxygen sensor voltage should vary quickly from about 200 to 800 mV. The rule of thumb is that the voltage should go below 500, and above 500 mV in an even pattern.

This is known as o2 cross counts. This is how many times the voltage crosses the middle specification of 500mv. If you see an oxygen sensor that has a fixed voltage or a voltage that is always below 500. You want to check the wiring to the sensor. The oxygen sensor wiring is underneath the vehicle and is easily damaged by road debris.

Another reason you may have a low or fixed voltage is the oxygen sensor is reading correctly, but the exhaust gases are not in the proper range. This could relate to a problem in the fuel management program.

Meaning the exhaust gases are actually lean or rich due to a failure of a fuel system component. A prime example example would be a leaky fuel injector, vacuum leak, or misfire condition. To clarify my point, if you set an o2 code this does not always indicate the sensors need to be replaced. What these codes do indicate is diagnosis is necessary.

When Do Oxygen Sensors Need Replacing

image of Oxygen sensors

The exception to this rule is if an automobile has extremely high mileage. Oxygen sensors can start to lose their accuracy at around 100,000 miles. Again, this doesn't mean the sensor needs to be replaced, but it's an indication sensor operation should be checked carefully.

Using the automotive scan tool can be interesting and fun. Reading data can be a great learning experience. Another bonus is plugging in and reading the data is a clean job. It won't cover you with grease, no knuckle busting and it's almost impossible to injure yourself performing the operation. Bookmark and share this diagnostic page after watching the video.





See Mark Gittelman's Awards & ASE Certifications on Google+.

I own a wide variety of automotive scanners for home and professional usage. See the ones I own plus a comparison of the features and benefits of each. The next link takes you to reviews of automotive scan tools.

My first page about this subject provides a few more common reasons the check engine light might pop on. Go to the page about auto scan tools.

This article is a little more advanced and requires an advanced scan tool that can read the data stream. Learn more about reading scan tool data.

Up next is the about us page. Find out more about the car mechanic that built this website and find more ways to get car questions answered.

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