How to use automotive diagnostic tools?

What to buy – and what to check

In the past, automotive diagnostic tools were too expensive. Before 1996, an independent technician could spend thousands of dollars on a tool that was compatible with only one vehicle. Even after the introduction of On-Board Diagnostics II (OBD-II), professional scan tools still cost thousands of dollars.

Today, you can purchase simple code readers for less than the price of a movie ticket, and the right accessories can even turn your phone into a scan tool. Since most of the information needed to interpret trouble codes can be found online, checking your engine light no longer requires an immediate visit to your mechanic.

Before buying an automotive diagnostic tool, it is important to realize that they are not some sort of magic panacea. When you plug in a check engine light code reader, or even a professional scan tool, it doesn’t automatically tell you how to fix the problem. In most cases, it won’t even tell you what the problem is. It will provide you with a fault code or several codes that provide a jumping off point in the diagnostic process.

What is Check Engine Light?

When your Check Engine Light comes on, your car is attempting to communicate in the only way that works. At the most basic level, the Check Engine Light indicates that some sensor (somewhere in the engine, exhaust, or transmission) is providing unexpected data to the computer. This could indicate a problem with the system the sensor is responsible for monitoring, a bad sensor, or even a wiring problem.

In some cases, the check engine light may come on and then eventually turn off automatically without external intervention. This does not mean that the problem has gone away, or that there is no problem in the first place. In fact, information about the problem is usually still available through a code reader even after the lights have been turned off.

How to get automotive diagnostic tools?

Code readers and scanners are only available from specialized tool companies, so they can be a bit difficult to obtain for the average car owner. This has changed in recent years, and you can purchase inexpensive code readers and scan tools from retail tool and retail stores, online retailers, and many other places.

You can even rent or borrow automotive diagnostic tools if you’re not interested in buying them. Some parts stores can always provide code readers for free, but know that you may be able to buy some parts from them if you can identify the problem.

Some tool stores and tool rental companies can provide you with higher-end diagnostic tools for much less than the cost of buying one. So if you’re looking for something other than a basic code reader, but you don’t want to spend the money, that may be an option.

The difference between OBD-I and OBD-II

It’s also important to understand the difference between OBD-I and OBD-II before buying, borrowing or renting an automotive diagnostic tool. Vehicles produced after the advent of computerized controls, but before 1996, were concentrated in the OBD-I category. These systems do not have much in common between manufacturers, so it is critical to find a scan tool specifically designed for your model, model and year.

Vehicles built after 1996 use OBD-II, which is a standardized system that simplifies the entire process. These vehicles all use a common diagnostic connector and a common set of fault codes.
Manufacturers may choose to go beyond the basic requirements to produce manufacturer-specific codes, but as a rule of thumb, you can use any OBD-II code reader on any vehicle built after 1996.

Finding where to insert the diagnostic tool

Once you have mastered the check engine light code reader or scan tool , the first step in using it is to locate the diagnostic connector. Older vehicles equipped with OBD-I systems place these connectors in a variety of locations, including under the dashboard, in the engine compartment, and on or near the fuse box.

OBD-I diagnostic connectors also come in a variety of shapes and sizes. If you look at the plugs on your scan tool, you should be able to get an idea of what to look for based on the size and shape of the diagnostic connector.

If your vehicle is equipped with OBD-II, the connector is usually located under the dash on the left side of the steering column. The location can vary from person to person, or it can be buried very deep. In some cases, you may find the diagnostic connector even covered by a panel or plug.

The connector can be rectangular or isosceles trapezoidal. It will also have sixteen pins configured in two rows of eight.

In rare cases, your OBD-II connector may even be located in the center console, behind the ashtray, or other hard-to-find location. If you have trouble finding the exact location, it is usually documented in the owner’s manual.

Using the Check Engine Light Code Reader

With the ignition key off or removed, you can gently insert the code reader plug into the diagnostic connector. If it does not slide in easily, make sure the plug is not upside down and that you have correctly identified the OBD-II connector.

With the diagnostic connector firmly inserted, you can insert the ignition key and turn it to the on position. This will provide power to the code reader. Depending on the specific device, it may prompt you for some information at that time. You may need to enter the VIN, engine type, or other information.

At this point, the code reader will be ready to do its job. The most basic device will provide you with any stored codes, while other scan tools will provide you with the option to read fault codes or view other data.

Interpreting Check Engine Light Codes

If you have a basic code reader, you will have to write down the trouble codes and do some research. For example, if you find code P0401, a quick internet search will show that it indicates a fault in one of the oxygen sensor heater circuits. This doesn’t tell you exactly what’s wrong, but it’s a good place to start.

Some scan tools are more advanced. If you have access to one of them, then the tool may be able to tell you exactly what the code means. In some cases, it will even provide you with troubleshooting procedures.

Next steps

Whether you are using a basic code reader or a fancy scanning tool, the next step is to determine the cause of your trouble codes. The easiest way to do this is to look for potential causes and troubleshoot each one in turn. If you can find the actual troubleshooting procedure, so much the better.

Using the previous P0401 trouble code as an example, further investigation will reveal that it indicates a faulty oxygen sensor heater circuit in the first row of sensors. This could be caused by a faulty heating element, or it could be a wiring problem.

In this case, the basic troubleshooting procedure would be to check the resistance of the heater element, confirm or troubleshoot the problem there, and then check the wiring. If the heater element shorts or shows readings outside the expected range, then replacing the oxygen sensor may solve the problem. If not, then the diagnosis will continue.

Finishing the Job

In addition to simply reading the codes, most check engine light code readers can perform a handful of other important functions. One such function is the ability to clear all stored trouble codes, which should be performed after a repair attempt. This way, if the same codes come back later, you will know that the problem has not actually been fixed.

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