What does it mean if my check engine light goes on and off?

What the Check Engine Light Does

Since 1996, motor vehicles have been equipped with the OBD-II (second generation) diagnostic system, an enhanced and standardized version of the previous generation. The OBD system—as it relates to the check engine light—monitors and controls the amount of emissions produced during the operation of your car by constantly checking and correcting input values to the appropriate systems with the help of sensors and actuators, including:

  • Engine coolant sensor
  • Oxygen sensor
  • Knock sensor
  • Camshaft and crankshaft sensors
  • Evaporative emissions (fuel vapors) sensor
  • Air meter sensor
  • Canister purge solenoid
  • EGR solenoids
  • Fuel injectors
  • Fuel pump
  • Idle air solenoid
  • Idle speed motor

Whenever the computer detects an abnormal condition through one of these, it sets a DTC in memory and lets you know by illuminating the light.

A check engine light warns you about emission-control related problems.

Photo courtesy of Rich Nacmias on Flickr

A check engine light helps you keep emissions under control.

Photo courtesy of Simone Ramella on Flickr

Types of Engine Light

So we agree that when the engine light illuminates it means there’s a problem with your car’s performance, right? But what kind of problem really? Let’s dig deeper.

Steady light: It means there’s a problem but it’s not an emergency. Nonetheless, you should schedule an appointment with a qualified service technician as soon as possible. Don’t wait for the problem to escalate and cause further damage.

Blinking light: It indicates a severe engine misfire. The emissions output and safety of the vehicle are affected. Such a misfire allows unburned fuel to be dumped into the exhaust system.

This dumped unburned fuel can quickly raise the temperature of the catalytic converter to a point where damage is likely. And that can only mean an expensive car repair.

What to do? If the engine light is constantly flashing, your can engine can be seriously damaged. Switch off the engine at the nearest safe place and have your vehicle checked.

Be warned that today’s automotive computers try to compensate when there’s a problem.

And as a result, you may not notice the declining performance of your car despite your fuel mileage suffering and your car emitting unacceptable levels of pollutants such as hydrocarbons.

Also, the check engine light should not be confused with the maintenance reminder or the service interval light.

These lights will always illuminate when a service is due because they are triggered by mileage, or amount of fuel consumed.


Disconnect Code Reader

Once code gathering or code clearing is complete turn the ignition key off, then grasp the connector firmly and pull gently outward unplugging the code reader from the ALDL data port. Replace the cover over the port if equipped to prevent any corrosion causing moisture that could cause damage to the connector. Once the code reader or scanner is disconnected find a cool dry place to store it in such as the top drawer of your tool box, that's where most mechanics keep theirs.


Should I Just Ignore It And Drive The Car As It Is?

You should definitely not be driving your car as it is. Just take it to your local mechanic. If you have the know-how and the right tooling then try to fix it on your own, although I would still recommend a professional mechanic. Especially if you do not know what you are getting into.

Don’t ignore that light

Mazor says that some people freak out when they see the check engine light. “They just put a piece of black tape over the dashboard light and keep driving,” he said. But Mazor adds it’s important to address problems indicated by the light promptly. Ignoring them could lead to larger, costlier problems later.

If the light comes on, Mazor suggests the driver check the gas cap. A loose gas cap sends an error message to the car’s computer, reporting a leak in the vapor recovery system, which is one aspect of a car’s emissions system. If the fuel cap is loose, tighten it and continue driving. Even so, it will take some time for the light to go off, he says.

What should you do if the check engine light comes on and it’s steady rather than flashing? The most obvious answer is to get the engine checked by a mechanic. But many people do nothing, perhaps fearing an expensive repair bill. Some drivers with older vehicles may want to squeeze out as many remaining miles as possible without visiting a service garage. But before they can pass their state’s vehicle inspection, they have to get the light turned off. And a state inspection is a good motivator for dealing with the problem. Ultimately, the engine and the emission control system are so interlinked that the health of the emission control system is a good indication of the general health of the car’s engine.

How to turn off the check engine light

Most code readers will allow you to turn off or reset the check engine light. But this action alone does not actually address the underlying problem. In many cases, the light will simply come back on later.


In this article we went deep and learned a lot about this issue with the check engine light that comes on and off. We also thoroughly explained the main culprits for this issue. And finally, we shared some DYI fixes that will make your life easier. If you are a beginner, it is better to leave it to someone that is more experienced to deal with these issues, like a mechanic. But if you think you are ready just dive into it and start doing some troubleshooting.

Recent Posts

Issues with an aftermarket alarm

An aftermarket alarm system can wreak havoc on your car if it’s not installed properly. It can drain the battery, trigger the check engine light, or even prevent the vehicle from starting. Then, when you least expect it, it’ll go off in the middle of the night because a leaf from an oak tree fell on the hood.

If the above issues sound familiar, you’ll need to have the alarm fixed, reinstalled, or replaced entirely by a competent mechanic. Getting it done right in the first place might cost a little bit more, but the peace of mind that comes with having a fully functional alarm is priceless.

Is it safe to drive with the Check Engine Light on?

The first thing that comes to mind when the check engine light comes on is whether it is safe to drive with check engine light on.

When the flashing check engine light comes on you need to pull over immediately.

Such a move is critical in ensuring that you do not cause further damage to major components of your car

Damaging major components such as the catalytic converter can significantly add to repair cost.

Have the car towed immediately to a mechanic shop for inspection.

A mechanic will use an OBD2 scanner to establish the source of the problem.

However, when the check engine light comes on without blinking you may need not to pull over and have the car towed.

What you should do is to drive to a convenient place, be it a parking zone, home, or to a mechanic shop and have the car diagnosed.

If you are a DIYer you can use an OBD2 scan tool to diagnose and fix the problem.

What does it mean when your check engine light blinks 5 times?

The most common cause of this is the key position. Often times when you turn the key to start the car but do not crank it, it will blink 5 times.

The reason for this is because you turned the key to ‘start’ instead of ‘run’ and once you turned it to run it stopped blinking. Something else that may cause it to blink is if your battery has just been disconnected.

If you disconnect your battery, usually when you reconnect it, and go to start the car, the check engine light will blink 5 times before going out again.

Test Your Knowledge!

For each question, choose the best answer. The answer key is below.

  1. This sensor won't trigger the Check Engine light because of a hard starting problem but the others will:
    • Faulty mass air flow sensor
    • Defective coolant temperature sensor
    • Faulty oxygen sensor
    • Bad fuel injector
    • Bad crankshaft position sensor
    • Bad idle speed motor

Answer Key

  1. Faulty oxygen sensor

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Not Safe to Drive?

The next set of situations are either right before or just after the check engine light has come on, and you hear or feel something strange in the way the engine or transmission is operating. The first thing to look for is the reading on the engine temperature gauge or if the engine temperature warning light is on, in this case you must pull over in a safe area and shut the car off. This will save the engine from serious internal damage. If you can feel the engine misfiring it can cause the catalytic converter to overheat and melt internally due to the unburnt fuel being processed which will require a catalytic converter replacement. The car's computer also monitors the automatic transmission and can tell if the transmission is slipping. This could be due to a loss of fluid in which case if you continue to drive the transmissions can burn up which would require a full transmission rebuild.

Personal safety should be your biggest concern. If you must pull over search Google for the closest tow truck company using your phone, also check their reviews. Likewise do the same for a repair garage in your area.


  • Reputable auto shops will not reset a check engine light without fixing the problem that caused the light to come on.

    Thanks! Helpful 6 Not Helpful 5

  • Consult a mechanic or repair shop if you need help resetting a check engine light or deciphering error codes.

    Thanks! Helpful 1 Not Helpful 4


Problem Fixed?

As we’ve seen, all these car issues can be fixed either by you or a mechanic. It’s a no-brainer that you can tighten a loose gas cap.

However, some issues will need you to take your car to a professional who with a scan tool will read and interpret the diagnostic trouble codes.

Want to try it yourself? Ok, but there’s one (potential) problem: the code testing procedure must be done in absolute sequence. Skipping some tests or performing steps out of sequence can make the entire process worthless.

Even close doesn’t count. Frustrating, right?

Maybe you’re wondering if there’s a better way to understand your car’s issues right away. Something that could monitor your car 24/7 while you’re on the road and alert you when there’s a problem – in plain English.

No more confusing check engine codes and other tech lingo.

A brilliant and affordable little device called GOFAR helps you monitor your car’s health AND gives you timely alerts (in plain simple English) when your car has a fault.

That way, you’ll deal with each problem firsthand before it becomes expensive. Understanding your car just got easier with GOFARCheck it out now.

Will the check engine light tell me when I should fix my car?

The check engine light provides an idea — sometimes precise, sometimes vague — of what’s wrong with a car. However, it does not replace a skilled mechanic or routine maintenance.

In other words, don’t wait until the check engine light comes on to get your car maintenance done. The ECU will not warn you that the water pump is about to fail, that one of the ball joints is worn, or that the A/C will stop blowing cold air in mid-August. Many people think that the check engine light serves the same purpose as a check-up reminder when it really alerts you that you’re probably due for a repair. By that point, the damage has already happened in many cases.

You can think of car maintenance as a two-step process. The first and most critical is routine, preventative maintenance. You should do these tune-ups on a schedule and not in response to any issues. The second is timely diagnostic maintenance which is responsive to changes like new sounds, smells, or feelings as you drive.

You also want to be familiar with your car’s basic needs, like how often to change the oil and coolant or replace brake pads. A little research into your specific vehicle and basic mechanics can save you time and money in the long run. If you’re consistent with a regular maintenance routine, you may never see that little orange engine light pop on at all.

Editors' Recommendations


Leave a Reply

Your email address will not be published.