Check Engine Light Flashing: Why It Happens & What to Do About It (2024)

Nowadays, our vehicles also let us know when there’s a problem with one or more of the systems that make them run.

All sorts of warning lights illuminate when an issue is detected by the vehicle’s computers, but no light is more ominous than the check engine light.

It’s bad enough when that light comes on, but it’s even worse when it starts to flash. A flashing engine light is a sign that there is a serious problem occurring, and one that shouldn’t be ignored under any circ*mstances.

Below, we cover everything you need to know and what you need to do if whenever your “Check Engine” warning light begins to blink.

What Is the Check Engine Light?

The check engine light is a small icon with a vehicle’s gauge cluster which illuminates if the vehicle’s ECU, or “Electronic Control Unit”, receives a fault code from one of its sensors, actuators, or systems.

This is a function of the On-Board Diagnostics system.

Starting in 1996, the EPA mandated that every vehicle sold should have a standardized system with which to monitor computer systems in vehicles. This is called On-Board Diagnostics II or OBDII.

An OBD II stores each error code received by the ECU, and can be read by an OBD2 scanner to show exactly what each fault code represents. After all of this is done, a diagnosis can be made.

Even if it is not currently illuminated in your car’s dashboard, an OBD II scanner has the ability to see previous fault codes sent to the ECU, and is the answer for how to reset the check engine light if you so desire.

What Would Cause the Check Engine Light to Come On?

The reason check engine lights come on is because of a non-adjustable event that occurs with a vehicle’s computer systems.

A flashing check engine light is usually a sign that several systems are failing, or one major system is being heavily compromised.

A blinking check engine light is a worst-case-scenario situation, and shouldn’t be confused with intermittent illumination.

Intermittent illumination occurs only when an issue is being actively detected, and could go off for several days at a time and then re-illuminate for several more days.

If it stays on, this is not something you should overlook, but is not necessarily something that signifies immediate danger or severe damage.

What Would Cause the Check Engine Light to Flash?

It will not usually flash, unless there’s a major problem occurring with the vehicle’s fuel or emission system.

The most likely issue that would cause flashing is when the catalytic converter is damaged because of the problem that’s occurring.

The following list discusses some of the most common problems that might cause this light in your dashboard to flash:

Engine Has a Misfire

An engine misfires when fuel is injected into the combustion chamber, the piston moves up to compress the air and gasoline mixture, but no combustion occurs.

This could happen for multiple reasons such as a fouled spark plug, a faulty injector or injector system, or even piston damage.

It’s the most common reason the check engine light starts flashing, as undetonated fuel could leak through the exhaust system and make its way into the catalytic converter.

Unburned fuel which reaches the catalytic converter could actually burn inside the converter itself and melt its interior structure, causing obstruction of exhaust flow.

This could also prevent the harmful exhaust gasses from catalyzing, thus causing a blown catalytic converter.

There Is an Ignition System Defect

The check engine light could start flashing if the spark plugs, ignition coils, or seals within the ignition system have failed or are leaking. This is one of the more common reasons a misfire could occur.

Oil can leak into the combustion chamber and prevent the spark needed for detonation, causing a misfire. Unburned oil can also have the same effect as unburned fuel, if it passes through the exhaust manifold and into the catalytic converter.

Spark plugs and ignition coils should be replaced regularly for this reason. An ignition coil generates electricity with spark plugs to ignite the air and fuel mixture in your car’s combustion chambers

Changing spark plugs, coils, or O-ring seals are both common maintenance procedures you can do at home to see if it solves the issue.

Learn more in How Often Should You Change Spark Plugs?

Engine Damage or an Engine Component Defect

Even if the catalytic converter is not directly affected by engine damage, it could also be the cause of the dreaded flashing light.

Timing chain, valve, and piston damage are rare causes for this, but they are among the most serious reasons this happens.

Most likely, there will be other signs of engine damage that appear before or while any warning lights illuminate, including loud engine noises, a shaking vehicle, or even engine cutoff.

Any engine component damage could cause the entire engine to fail, requiring a replacement.

There Is a Fuel System Defect

Any time a fuel system component fails, a sensor is sending wrong information to the ECU, or another system sensor is receiving faulty information, there is a possibility that your check engine light could start flashing.

Defects in fuel system components are a primary cause of an engine misfire. Fuel is delivered to the engine in varying amounts depending on factors such as throttle position and air intake. If any of these sensors were to fail, this could cause too much fuel or less than is actually needed to reach the engine.

Fuel Leak

A fuel leak is another culprit. Fuel could be pumped to the engine, but never received by the engine. Fuel could also be leaking around or inside the engine itself.

Faulty Oxygen Sensors

A faulty oxygen sensor could fail to deliver the correct amount of fuel to the engine.

Even a working oxygen sensor could send what it believes to be the correct amount of fuel to the engine, because an airflow sensor is providing incorrect readings.

Faulty EVAP System and EGR Valve

Both the EVAP system and EGR valve could be faulty.

EVAP stands for Evaporative Emissions Control, and is a system that neutralizes gasoline fumes emitted by a vehicle’s gas tank.

EGR stands for Exhaust Gas Recirculation, and is designed to recirculate exhaust gasses to a vehicle’s intake in order to mitigate harmful emissions.

When either of these systems fail, a vehicle’s emissions system is compromised and could result in a check engine light blinking or flashing.

Vacuum Leak or Gasket Failure

Anytime air, oil, or gasoline bypasses a sensor and leaks into places it shouldn’t, your engine and other components are at risk of failure.

A vacuum leak could cause additional air to seemingly enter the engine, causing the ECU to overcompensate and send additional fuel when it isn’t needed.

This again could cause a misfire due to excess amounts of fuel within the combustion chamber.

Likewise, a gasket failure could cause coolant and oil to leak into the engine and eventually the exhaust, possibly resulting in catalytic converter failure.

Emission System Fault

A catalytic converter converts car exhaust emissions and pollutants into compounds that cause less harm to the environment. Catalytic converters, however, can wear out with age and become clogged over time.

An overheating engine is another common cause of catalytic converter failure, and can be compounded by an oxygen sensor failure.

Faulty ECU or Other Sensors

ECU failure is rare, but can occur. If it does, there will probably be a host of other problems that accompany it at the same time.

Apart from the ECU, there are anywhere between 60 and 200 different sensors working to keep your car performing properly.

Not every single one of these is vitally important to emissions, fuel delivery, or engine function, but one that fails could cause the ECU to illuminate the light or make it flash.

In these situations, using an OBD II scanner will tell you which sensor is malfunctioning.

Your Gas Cap Is Loose

Consider yourself very lucky if you find yourself in a situation where this happens because of a loose gas cap.

Most vehicles have a separate gas cap light that can also flash if there is a major system malfunction, but simply tightening it or screwing it back on can eliminate the problem.

Again, this sounds ridiculously simple (and it really is), but don’t laugh it off! You’d be surprised at how many times this turned out to be the culprit.

Broken Engine Mount

Engine mounts can wear out and snap off, whether due to wear and tear or because your vehicle has been well used.

This could cause severe shaking, which – in turn – could result in seals, other bolts, and wiring disconnecting.

If you experience severe shaking in your car and the check engine light begins to flash, stop and turn off the vehicle to prevent damage from occurring.

Electrical Short or Other Electrical Issue

Wiring and electrical issues can cause a whole host of problems for a vehicle, and the lack of electricity could do the same.

Anytime a sensor stops receiving information, it can no longer transmit information to the ECU and will cause a fault code.

If the ECU can’t receive the data it needs, it could do anything from make the check engine light flash to shut off the vehicle, depending on which sensor isn’t receiving any information.

A disconnected wire or lack of battery or alternator power could also cause this to happen, but is unlikely to do so.

What Should You Do If the Check Engine Light Is Flashing?

If this starts happening while you are driving, you should take the vehicle to the closest certified mechanic or local repair shop to have them look at the fault codes.

If the vehicle starts behaving erratically, find the closest pull-off area so you can safely park and turn it off. The same should be done if there are unusual noises or if the vehicle starts shaking.

If it starts blinking while you are parked, you can still opt to drive it to the nearest repair shop, but towing it is a safer option.

Under no circ*mstances whatsoever should you drive the vehicle for extended periods of time or long distances with the light flashing. This is very important, both for your safety and your vehicle’s well-being!

Take It to a Mechanic

Because a flashing check engine light is often the sign of a serious issue, you often won’t be able to fix the problem yourself.

Even if you have your own OBD II scan tool, mechanics usually have much more expensive versions that pinpoint issues more accurately.

The Sooner, the Better

Catalytic converter damage, engine component damage, and sensor issues often require replacement rather than simple repairs.

The sooner you diagnose the underlying issue, the greater the chance that irreversible damage will be avoided.

Don’t Panic

Never panic when you notice this is happening, especially if you’re driving. Panicking while in traffic is one of the worst things you can do for yourself and others around you.

Instead, simply find the best and safest place to pull off the road.

It’s Not Always a Huge Problem

Don’t always assume the worst – because oftentimes, it could be a simple fix.

The On-board Diagnostics system in your vehicle is designed to alert you to problems in order to prevent something worse from happening.

The most common cause is a loose fuel cap, and – as discussed above – fixing this is ridiculously easy.

Always do whatever you can to check anything that might be “too obvious.”

You may not be able to tear your ride apart on the side of the road, but you can inspect the engine, check for any leaks, and secure any wiring, hoses, or filler caps to see if that helps.

If it does, then congratulations! You’ve just saved yourself a lot of time and – very possibly – a whole bunch of money in repair costs.

Wrapping It Up

Nowadays, there are so many moving parts in any vehicle, and so many computer systems that work together to keep them running properly.

Most of them intertwine with one another and have a domino effect if just one fails.

Rarely is there ever only one issue that will cause that dreaded flashing light. Sometimes, the codes received by the ECU don’t even reach the main source of the problem, but are side effects of a larger issue.

Regardless of what exactly is happening to your vehicle, you should never ignore this event.

Ignoring it could cost you thousands of dollars in damage, and a much bigger problem on your plate than what you already had.

Instead, doing whatever it is you can do to inspect your vehicle can solve the entire issue – oftentimes with just a simple twist of a cap or tightening of a screw.

Whatever you do, though, always remember never to panic! And always keep in mind that a mechanic is always standing by for help if you need it.