Check Engine Lights can show a minor problem or indicate a larger issue.

What Does a Check Engine Light (CEL) Mean?

A check engine light illuminating unexpectedly can quickly ruin a nice drive. Often, the car seems to run fine, but drivers should still be concerned. Fortunately, it is very easy to find out why a check engine light has illuminated. Many companies make scanners for identifying codes stored by a car’s computer when the check engine light comes on.

What is a Check Engine Light?

The evolution of the check engine light -often abbreviated as CEL- goes back several decades. In old cars, drivers had numerous gauges that provided real-time feedback about engine conditions. Many vehicles had a gauge that showed oil pressure and another that showed amperage or voltage. Car manufacturers began reducing the size of instrument panels and increasing the size of gauges to make them more readable. Today, many vehicles will have a speedometer, a gas gauge, a temperature gauge, and not much else. Over the many years before computer-controlled engine management systems, dash lights for oil pressure, braking problems, and other indicators of engine trouble became common.

During the 1980s, government regulation in the United States led automobile manufacturing companies to begin using standardized computer systems for analyzing engine problems. Car manufacturers created a standardized system called OBDII, short for On-Board Diagnostics. OBDII was primarily developed by car companies as a means of checking emissions controls to improve engine performance and reduce pollution. Every vehicle sold in the U.S. since 1996 has included an OBDII or similar system for identifying poorly performing components.

obdii port
The connector for an OBDII scanner is a unique design. Here, an ethernet plug is shown for comparison.

Today’s vehicles have numerous computerized sensors. OBDII systems are capable of storing codes that result from faults in the engine, transmission, braking, cooling, and even tire pressure systems.

How Can You Figure Out Why the CEL is On?

It is really easy today to find out why a check engine light is on. Most auto parts stores will scan your car for free and provide a list of codes that are stored in the computer. Scanners for use by the DIY mechanic are easily available and are a low-cost tool every mechanic should have in their toolbox.

OBDII scanners work by plugging into a special port under the dash of a vehicle. Most cars will have the port either below the ignition switch to the right of the steering wheel or on the left side near the kick panel. An OBDII scanner typically takes a few minutes to read the stored codes and return a list of faults.

obdII port location
An OBDII scanner is an essential tool for identifying problems with computer-controlled vehicles.

Many scanners do little more than display the code -typically a letter and four numbers- which leaves the technician to figure out the meaning of the code. This is where things can get tricky for the home mechanic.

Is it Safe to Drive a Car with a CEL On?

CEL codes returned by a vehicle’s computer can range from minor to severe, and it can be a challenge to figure out which is which. In many cases, an OBDII scanner will return only generic codes that could point to one of several problems. Some vehicles even use multiple CEL displays to identify significant problems from minor ones.

Drivers should find out why a check engine light is on as soon as possible. Owners should not be drive cars with a check engine light on. DIY mechanics that have their own scanners can check the code immediately. You can save thousands of dollars on expensive repair bills by fixing problems before they become serious.

What is the Best Scanner to Use?

OBDII scanners come in all shapes and sizes, and from prices in the really cheap to really expensive categories. Some scanners do more than others. Some scanners are very basic. There are essentially two types of scanners common on the market today. One type is a removable handheld tool intended to be used with the vehicle parked. The other is plugged into the OBDII port and sends real-time feedback to linked smartphones. Both have advantages.

Handheld Scanners

The most common type of OBDII scanner is the handheld, removable type. Drivers can test any car made after 1996 with these types of scanners. The Innova P6100 scanner is a great example of a handheld unit that can read and display numerous types of codes on almost all vehicles. A really nice feature of this particular scanner is the indicator lights that help to provide information about the severity of a problem.

innova p6100
The Innova P6100 is an excellent hand-held OBDII scanner that provides lots of useful information.

Handheld scanners are particularly useful for DIY mechanics that have multiple cars or use their scanner on other drivers’ cars. These scanners provide reliable information about the codes stored by the computer. Some -like the Innova P6100- even give drivers information about the most likely causes of a check engine light beyond just the code that is returned. This allows the DIY technician to easily identify the most likely culprit and solve the problem without buying a bunch of unnecessary parts.

Plug-in Scanners

OBDII scanners that are plugged in full-time have become more common in recent years. Users can link these scanners to a smartphone. A really popular option is the FIXD scanner. The device is simply plugged into the port and is left there while the car is driven.

obdII scanner
Plug-in type OBDII scanners such as the unit from FIXD look similar to this generic design.

Plug-in scanners are really helpful for identifying problems that happen while driving. The cost of plug-in scanners has really started to drop in the last few years, and these scanners are becoming more common. A plug-in scanner is most helpful for drivers who have one car that needs monitoring. A plug-in scanner like the unit from FIXD is a great option for a daily driver vehicle that needs to run right all the time.

Knowing When a CEL is Serious

Most often, a serious check engine light will be accompanied by obvious problems with the car. Maybe the engine sounds strange or is smoking, or maybe the transmission isn’t shifting. This isn’t always the case, though. A potentially serious problem that is common on newer cars are faults related to the O2 sensors. This can be a potentially serious problem because the O2 sensors are responsible for telling the computer how much to mix the fuel and air the car needs to run. When this mixture is incorrect, it can very quickly lead to catastrophic failures and high-cost repairs, but a driver may not even notice a difference in the way the car runs until it is too late.

bad o2 sensor
A check engine light will tell the driver when O2 sensors are failing. Driving with faulty O2 sensors can cause irregular running conditions and can lead to catastrophic engine failure.

Drivers should never ignore a check engine light. Most of the time, repairing a vehicle that has a minor problem will be cheaper and easier than repairing serious damage. In too many cases, drivers do not fix problems and simply keep driving their car until the engine fails.

A low-cost OBDII scanner is a great investment that can quickly pay for itself by preventing serious engine damage that results from drivers not knowing what the problem is.

Check out how you can easily see why your check engine light is on right here.

About Derek F

Derek grew up in Southern California and started working on cars when he was a child. He learned from his father and grandfather how to make basic repairs and maintain cars correctly. Derek rebuilt his first engine at 15 years-old, beginning an automotive career that took him to many interesting jobs. Derek has worked as an automotive detailer, managed parts warehouses and auto parts stores, and worked as a mechanic for several years doing brake and suspension work. While pursuing a bachelor’s degree in government journalism, Derek worked for an auto museum where he started to write about cars. Today, Derek uses his expertise gained from many years of practical experience to help educate DIYers and share interesting knowledge about various types of automotive repair and service. Writing about cars helps fund his numerous classic car restoration and customization projects.

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