It’s everyone’s worst nightmare – the Check Engine Warning Light illuminates on the dash. This common occurrence causes a sinking feeling in your gut and causes you to go into a deep panic mode.

Before you go too deeply into that spiral, remember that some minor issues can cause your Check Engine Light to come on. We look at the meaning of the Check Engine Lights, the reasons it happens, and how to fix them. 

Check Engine Light Meaning

Check Engine Warning Light

The Check Engine Light is the warning sign that lights up on your car’s dash when something is wrong with your engine. It was once referred to as the Malfunction Indicator Lamp. 

In 1996, automakers began standardizing all systems with the OBD-II protocol. This system provides a list of diagnostic trouble codes that can be read through a universal connector. 

The Check Engine Light illuminates when the car’s computer recognizes a problem. It can be an orange, amber or yellow light, depending on the car manufacturer. 

The Check Engine Light can shine steadily, which indicates there’s an issue that must be checked out. These problems aren’t generally immediate concerns, but you should get right to the mechanic.

However, the Check Engine Light that flashes off and on is indicating a critical fault. At this point, you should pull over and have the car towed. 

Some people confuse the Check Engine Light with the service light. This important indicator has a wrench-like shape and says, “Service Now” or “Service Soon.” This light only serves a reminder to get your scheduled maintenance performed and doesn’t indicate an issue.

Causes of Check Engine Light

  1. Loose Gas Cap
  2. Failing Oxygen Sensor
  3. Failing Catalytic Converter
  4. Defective Spark Plugs or Wires
  5. Failing Mass Air Flow Sensor

Because the Check Engine Light is responsible for alerting you to any trouble, it can indicate small issues to major repairs. Here are the five most common reasons this indicator turns on.

Remember that a lot more things can cause the light to come on! Check further down how to diagnose it properly!

Loose Gas Cap

Open Fuel Tank Cap

The car’s gas cap seals the fuel system, so the tank receives the right amount of pressure. When you don’t apply the gas cap tightly enough or it is damaged, the pressure could be off in the fuel system. 

Thankfully, this is one of the easiest fixes. You can either secure the gas cap or replace a damaged one for just a few dollars. 

Failing Oxygen Sensor

O2 Sensor On Cat

When an oxygen sensor begins to fail, you might also notice a decline in the fuel economy. Many vehicles contain four oxygen sensors, and any of these can fail.

Depending on the make and model of your vehicle, the oxygen sensor replacement cost could be around $250. 

RELATED: 5 Symptoms of a Bad Oxygen Sensor (O2)

Failing Catalytic Converter

Clogged Catalytic Converter

Typically, the catalytic converter fails because you haven’t performed regular maintenance or you ignored other issues. If the spark plugs, wires or oxygen sensor require replacement, you should do it right away, or you could end up with this costly repair.

Catalytic converter replacements cost $1,000 or more in most situations. 

RELATED: 8 Symptoms of a Bad Catalytic Converter

Defective Spark Plugs or Wires

Spark Plug Misfires

When the spark plugs corrode or wear out, you will notice engine performance issues. It’s also possible that the engine won’t start at all. That’s because this critical part supplies the spark needed for ignition. 

The spark plug wires are just as critical, supplying the spark created from the coil to the plugs where it can ignite the air-fuel mixture. Both of these parts are replaced as part of a regular tune-up. Check your owner’s manual to follow the manufacturer’s recommendations. 

RELATED: 6 Symptoms of Bad Spark Plugs

Failing Mass Air Flow Sensor

Cleaning Maf Sensor

The mass air flow sensor keeps track of how much air enters the engine. Then, it uses these calculations to determine how much fuel needs to mix in. 

When the MAF sensor starts to go bad, you might notice a drop in fuel economy because the engine can’t run efficiently anymore. For most cars, the mass air flow sensor replacement is only between $100 and $400. 

RELATED: 8 Symptoms of a Bad MAF Sensor

How to Fix Check Engine Light

Mechanics Diagnose Car

To fix a Check Engine Light that is on, you will follow a few basic steps. 

  1. Buy an OBD Reader
  2. Scan for Engine Codes
  3. Search the Engine Code
  4. Replace the Defective Part
  5. Erase the Code

Buy an OBD Reader

It isn’t expensive to buy your own OBD code reader. With this handy tool, you can check common engine faults without paying a mechanic.

If you don’t want to buy an OBD reader, you can check with your local parts store. Many of the nationwide locations will check the codes for free.

Scan for Engine Codes

Under the driver’s side dashboard, you will see a trapezoid-shaped port. That’s where you want to plug in the code reader. Make sure the engine and key are off when you plug it in.

However, once the scanner is hooked up and on, you want to turn the key to your vehicle on but leave the engine off. Press the scan button and watch the codes that come up. 

Search the Engine Code

You can take your code to the internet to find the cause of your fault. At Mechanic Base, we keep our readers informed of the most common trouble codes

If you can’t find the information you need online, consider calling your local dealership for help.

Replace the Defective Part

Once you know what the problem is, you can purchase the necessary replacement parts and install them. Obviously, some of the repairs are going to cost a lot less than others, such as a replacement gas cap versus a catalytic converter.

However, you should never prolong a repair, as it could lead to more serious issues down the road. 

Erase the Code

Once everything is fixed, it’s time to erase the codes. Plug your scanner back in and hold down the erase button. 

You might need to confirm the changes. We recommend rescanning the engine to be sure they are gone. You will also see the Check Engine Light go off.

If you are repairing an issue to pass a smog check, take your vehicle for a few drives before getting retested. Many technicians can tell if you have recently deleted a code, so it’s best to drive for at least 50 miles first.