The car code reader is one of the simplest car diagnostic tools . They are designed to communicate with the car’s computer and report trouble codes that can cause an engine check and other problems.

How does a car code reader work?

Code reading systems OBD-I and OBD II operate in essentially the same way, as they control different sensor inputs and outputs. If the system determines that something is out of specification, it sets a «DTC» that can be used in diagnostic procedures. Each code corresponds to a specific error. There are also different types of codes (i.e. hard, soft) that represent both ongoing and intermittent problems.

Automotive OBD-II code readers are generally inexpensive, but some parts stores and stores will read the codes for free.

When a DTC is set, a special indicator on the dashboard will light up. This is a Malfunction Indicator Lamp (MIL) which is also called Check Engine Light. Basically what this means is that you can plug in a car code reader to see what the problem is. Of course, some codes do not turn on the check engine light.

Every OBD system has some type of connector that can be used to get codes. On OBD-I systems, this connector can sometimes be used to check codes without car code reader. For example, you can connect ALDL connector GM, and then check the flashing check engine light to determine which codes have been set. Similarly, codes can be read from OBD-I Chrysler vehicles by turning the ignition key on and off in a specific pattern.

In other OBD-I systems and in all OBD-II systems, fault codes are read by connecting an automotive code reader to the OBD connector. This allows the code reader to communicate with the car’s computer, retrieve codes, and sometimes perform a few other basic functions.

How to use a car code reader

To use the car code reader, it must be connected to the OBD system. Each OBD-I system has its own connector, which can be located in multiple locations. These connectors are often located under the hood in close proximity to the fuse box, but can also be found under the dash.

In cars that were built after 1996, the OBD-II connector is usually located under the dashboard near the steering column. In rarer cases, it may be located behind a panel in the dashboard, or even behind an ashtray or other compartment.

obd2 car code reader connector

OBD-II connector. The port you’ll usually find under your dash is usually the same shape, but some are rectangular.

Here are the basic steps to use the car code reader:

  1. Find OBD port .

  2. Paste OBD connector code reader to the OBD port.

  3. Turn on the code reader if your device does not turn on automatically.

  4. Turn the car’s ignition key to the accessories .

  5. Follow instructions on the screen code reader.

The specific procedure may differ from one code reader to another. Many of these devices are very simple and are designed to turn on as soon as they get power from the OBD port. Others have specific procedures that you must follow, in which case it is important to refer to the instruction manual.

What can a car code reader do?

Once the OBD connector is found and connected, the car code reader will connect to the car’s computer. Simple code readers can be powered through an OBD-II connection, which means plugging in a reader can turn it on as well.

At this stage, you will usually be able to:

  • Read and clear codes.
  • View the identifiers of the main parameters.
  • Check and possibly reset the readiness monitors.

Specific options vary from one car code reader to another, but at a minimum, you should be able to read and clear codes. Of course, it’s a good idea to avoid clearing codes until you’ve written them down, after which you can view them in the trouble code table.

Using a code reader to clear trouble codes also resets the readiness monitors. Most emissions and smog testing businesses look at readiness monitors and won’t let your car through if they’ve been reset. If you are clearing your codes after a repair is completed, it is important to test drive your vehicle with a combination of city and highway traffic so that the readiness monitors have a chance to work.

Limitations of the car code reader

While automotive code readers are a great starting point for your diagnostic routine, the same DTC can have any number of different causes. That’s why code readers are less useful than scanning tools .

When a professional diagnostic technician uses a code reader, they often have experience with this type of code, which gives them an idea of ​​which components to test. Many professionals also have much more expensive and complex scanning tools which come with huge knowledge bases and diagnostic instructions.

If you do not have access to such a tool, you can view the underlying fault code and troubleshooting information online. For example, if your vehicle has an oxygen sensor trouble code, you need to find the oxygen sensor testing procedures for your vehicle make and model.

ELM327 vs car code readers

The ELM327 scanning tools are an affordable alternative to basic car code readers . These devices use technology ELM327 to interface with your car’s OBD-II system, but they don’t have built-in software or a display.

Instead, the ELM327’s scanning tools are designed to provide an interface between your tablet, smartphone or laptop and your vehicle’s computer. Some mobile apps allow you to use the ELM327 scan tool and your phone as a code reader, and better software often provides you with a more powerful interface and diagnostic information.

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