What to Do When Your Check Engine Light Comes On

You could be driving down the highway, starting up your car in the morning, or pulling into a parking spot at the grocery store when all of a sudden you see the Check Engine Light (CEL) turn on. The yellow, usually central light on your gauge cluster. It could happen to anyone at anytime, no matter how new or old your vehicle is. It's arguably the most misunderstood indicator light on your dash and can mean a number of things, both severe and minor. So what do you do when you see this light come on? Let's start with helping you understand what the Check Engine Light is first, and why it's there in the first place.

What Does the Check Engine Light Do Anyway?

The check engine light is one of the many systems apart of your car's OBD (vehicle's onboard diagnostics) system. Today's cars have a number of monitoring and control systems that regulate things like fuel mixture, engine timing, performance, shifting, braking, and more. Originally, the OBD sensors and systems were designed in the 1980s to help identify problems with your cars, like a faulty sensor or engine misfire, so that technicians can easily diagnose and fix the problems. They were pretty primitive though and offered relatively limited information.

Today, OBD II is used, and its required under federal laws to regulate vehicle emissions. OBD II not only monitors many of the systems and sensors in your car, it now also acts like an emissions monitoring station. Today, the Check Engine Light only appears when there's a sensor or system on your vehicle that is effecting the emissions system. This can be a problem as little as a loose gas cap, and as big as a misfiring engine or faulty camshaft sensor.

In addition to turning a light on in your dashboard, it also logs a code in the computer called a “trouble code”. These codes can be read with an OBD II Scanner or Reader, and typically will point you in the direction of what the problem is and what part to fix.

What Do You Do When Your Check Engine Light Comes On

First off, if you see your CEL turn on check to see whether it's blinking or if it's solid. Typically, if the light is blinking it means that your engine is misfiring. Basically this could mean that your car is dumping unburnt fuel into the emissions system, which is triggering the light. Instead of blinking, some cars will identify misfires with a red light instead. If you see this, there may be a larger underlying problem to your car and you should take it to your mechanic as soon as possible, or use an OBD II Scanner to identify and fix the problem before you continue to drive your car. If you do need to continue driving, lower your speed and RPMs and try to reduce the load on your vehicle.

If the light isn't blinking or red, then the problem is likely not an emergency. However, ignoring the problem may have longer term effects on your vehicle and could cost you money in the long run. Here's a few steps to follow to diagnose your car's check engine light:

1. Check for a serious problem – Pull the car into a safe area where you can do a quick walk around to look at the car. Pop the hood and look for leaks or loose hoses. Ensure that your car is safe to drive!
2. Use an OBD II Scanner – If you have an OBD II scanner or reader, put it to use! Plug it in and run the system check to find the “trouble code(s)” that are stored in your car's computer. Typically the tool will provide a code (for example P00142). This code will identify the part that's faulty. More advanced scanners will tell you what part that needs to be replaced. In any case, the best thing to do once you've found the code is to research it on Google by typing in the search: “<year> <make> <model> <code>”. Year, make and model should match the car that has the code, and the code is what appeared in your scanner. In many cases, there are a number of forums where other people have had the same problem and sometimes even write-ups on how to fix it. If you don't have an OBD II scanner or reader, you can find a few that we recommend here. There are many that are cheap and will get the job done.
3. Check your gas cap – Remember, the CEL is mainly to identify emissions-related issues. Something as simple as a loose gas cap could trigger it to turn on. Turn your vehicle off, tighten your gas cap, and then restart your vehicle to see if it fixes the problem.