Tips To Diagnose A Check Engine Light

You love your car, but nothing tests that love like the sudden appearance of the check engine light. Suddenly, your faithful ride turns into a potentially costly repair bill just waiting to jump out and raid your bank account. For many drivers, that simple dash light is one of the most stressful things that can appear in their car. Luckily, a check engine light doesn't have to spell doom and, in most cases, it may point to a relatively simple and inexpensive problem. Step one is figuring out just what the light is actually trying to tell you.

Understand the Reason Your Light Turned On

Your check engine light is part of your car's OBD (on-board diagnostics) system. This is a standardized system for reporting data from the car's computer. The majority of this data is collected from various sensors throughout your car, and originally it was focused primarily on emissions controls. As cars have advanced, more and more data is piped through the OBD system. When your check engine light illuminates, it means that one or more trouble codes are being reported by sensors in your car.

Get the Codes Read

Of course, knowing that there is a trouble code stored by your car's computer isn't much help if you don't know what it means. Some newer cars can report trouble codes using the onboard infotainment system, but if your car doesn't have this feature then you will need to have the code read. Believe it or not, this won't require a trip to the mechanic. For getting the code read yourself, you generally have two options:

  • Take your car to an auto parts store
  • Buy a cheap OBDII reader

The first option is easy and free, but it can be inconvenient if you are regularly checking up on your car. Surprisingly, reading the codes yourself isn't difficult or expensive. OBDII readers can be purchased for less than $20 and they simply plug into a port that is usually located below the steering wheel. Modern OBDII readers pair your smartphone and will report trouble codes directly.

Research Your Codes

In many cases, the codes that you pull from your car will point you to the exact problem. OBDII trouble codes commonly indicate a sensor failure and the code will direct you to the sensor that has failed. If the code is more ambiguous, then you will need to bring your car to a mechanic or begin to do more research yourself. For complex problems, there will often be a large number of codes and it will be necessary to treat them as clues for uncovering the true source of the problem.

If you do see a large number of codes, it is important not to panic. Often, a minor problem can cause many sensors to report erroneous data. This can lead to a huge number of codes that do not actually indicate a problem with other systems. In other cases, issues that are causing your engine to run poorly (such as misfires) will trigger many unrelated codes. For this reason, check engine lights with unclear causes often warrant a visit to an auto repair professional.

Don't Clear the Codes!

It can be tempting to simply clear the codes if you have an OBDII reader, but this is usually a mistake. By clearing the codes, you are removing important information that can be used to diagnose your car's problem. In most cases, the codes will return in short order and the check engine light will simply illuminate again. Even worse, if your car is due for an emissions inspection, the recently cleared codes will cause your car to automatically fail.

Rather than clearing the codes, treat any light as a mystery that needs to be solved. Even without apparent driving issues, a check engine light means that something in your car is reporting a problem. Determining the problem and having it fixed can save you time, money, and trouble for the future.