A vehicle’s check engine light (sometimes abbreviated CEL) can indicate dozens of issues. Unfortunately, many of those problems can result in serious damage if not addressed immediately. Drivers tend to ignore the signal, and generally speaking, that’s a costly mistake.
By law, modern vehicles are equipped with computers that track the function of their emissions control systems. The computer triggers the check engine light when the system has issues. If there’s unnecessary pollution or the engine malfunctions, you’ll see the CEL. The computer also creates a log of the error, which is essential for diagnosing and fixing the underlying issue.
A steady check engine light can be a serious symptom. It can also show a minor problem like a loose gas cap or a busted oxygen sensor, which you can fix on your own.
However, if a check engine light flashing or blinking, the engine may be misfiring. Driving the vehicle in this condition can cause permanent damage (and a hefty repair bill). If your vehicle has a flashing CEL, here’s everything you need to know to address the problem.
Table of Contents
- Common Causes of a Flashing or Blinking Check Engine Light
- Determining the Cause of Check Engine Light Flashing
- The Bottom Line: A Blinking Check Engine Light Is a Serious Symptom
Before you get too concerned, consider whether your service engine light is flashing for a few seconds or blinking at a steady pace. If the check engine light comes on temporarily or under certain specific conditions (for instance, over a certain RPM), the situation might not be serious. Visit a mechanic or an auto parts store to read the car’s computer with an on-board diagnostics (OBD2) scanner.
Take this action as soon as possible — even if the check engine light turns off on the way to the mechanic. Your vehicle’s computer will store the ODB2 code, so you don’t need to wait for an illuminated CEL to get a diagnosis.
Common issues that cause the check engine light to blink flash intermittently include:
- Low fluids
The check engine light may trigger if your vehicle is low on coolant, power steering fluid, oil, brake fluid, or anything else. This is more common on older vehicles, but it’s a simple fix: Check your vehicle’s fluids or take it to a mechanic.
- Fuel ignition system issues.
If the cylinders of your engine aren’t igniting fuel properly, you’ll probably notice decreased power. That’s sometimes accompanied by other symptoms. Your vehicle might shake, especially when idling. Common causes include a failing spark plug, weak ignition coil, or bad plug wire. More serious fuel ignition system problems include dead fuel injectors, bent valves, and a leaking head gasket.
- Poor electrical connections
Your vehicle’s emissions control system monitors signals through electrical signals. Damaged wiring can certainly cause a check engine light. If your vehicle has electrical issues, you might not notice any change in performance, and the CEL might not stay lit consistently.
Still, electrical issues can interfere with your vehicle’s ignition and cooling systems. You should avoid driving until you’ve located the source of the problem.
We’re just scratching the surface here, as hundreds of issues can cause an intermittent CEL. To definitively diagnose the issue, you’ll need to find an ODB2 reader.
The good news is that most shops will read your codes for free, and if you’re a do-it-yourselfer, you can pick up a basic OBD2 reader for under $50. Write down the code and consult a mechanic to determine whether you can safely drive until you’re able to get the problem repaired.
Determining the Cause of Check Engine Light Flashing
If the check engine light blinks steadily, it means that the vehicle is trying to get your attention because the engine is misfiring. In other words, it’s not operating at its full potential, which doesn’t just mean a loss of power; a misfiring engine can sustain serious damage even while idling. Turn the vehicle off as soon as possible and have it towed to a mechanic. They’ll read the OBD2 codes to determine the next course of action.
So, why is your engine misfiring? Some common causes of a blinking check engine light include:
- Compression loss
Engines function by compressing a fuel-air mixture and igniting it. If the engine can’t carry out the compression stroke properly, your vehicle won’t be able to create enough power. Issues with the piston rings, cylinder head gaskets, valves, seats, and seals can all cause compression loss. That causes the engine to misfire.
Most modern vehicles will generate an OBD2 code that indicates the source of the compression loss to some degree. For example, a cylinder misfire code P0302 indicates a misfire in cylinder 2. Your mechanic might still need to perform a manual compression check to accurately diagnose the problem.
- Ignition system issues
As we discussed earlier, ignition system issues will prompt a check engine light. If your light is flashing steadily, the situation is serious. The most common ignition system issues include failed spark plugs and damaged fuel injectors. These issues are more common for high-mileage vehicles.
If you’re able to locate the cylinder with the misfire, replacing the ignition coil or spark plug could fix the issue. Don’t take this step before performing diagnostic tests. Otherwise, you could end up spending time and money on an unnecessary fix. Worse, you could accidentally make the problem worse by operating the engine.
- Temperature sensor issues
The coolant temperature sensor keeps your engine from overheating. When it fails, it stops sending an electrical signal to your car’s diagnostic computer, prompting a code. Temperature sensor issues can cause imbalances in the vehicle’s fuel-air mixture. That sometimes causes black exhaust smoke.
If your vehicle has one of these issues, you’ll probably notice performance issues. The vehicle might start sputtering, the engine might sound louder than normal, or you might encounter issues when accelerating. The car might seem to shake and you might hear loud explosions coming from the engine.
Needless to say, these are serious symptoms that require immediate attention. Misfires put tremendous stress on nearly every one of a vehicle’s essential systems.
How Much Is It to Fix a Misfire?
That depends on the cause of the misfire. A blinking check engine light could cost anywhere from under $100 for a spark plug replacement to several thousand dollars for a new catalytic converter.
Factors that affect pricing include your vehicle’s make, model, age, mileage, your zip code, and the extent of the damage. Don’t be afraid to get several quotes from qualified mechanics to keep your costs as low as possible. Remember: The longer you operate your vehicle, the higher the potential for serious damage.
Can Low Oil Cause a Misfire?
If your check oil light came on at the same time as your CEL, or if it had been lit for a while when the new symptom started, the problems could be related. Oil lubricates your engine, and running your engine with low oil pressure will cause major damage.
The bad news: Adding oil probably won’t get rid of the check engine light, and by the time the CEL triggers, you’ve got bigger issues than low oil. If you noticed a low oil warning before you noticed the check engine light, be sure to tell your mechanic.
Once again, you probably shouldn’t drive a vehicle if the check engine light indicator is lit — at least until you’re able to diagnose the problem. With that said, many drivers ignore engine issues, hoping that they’ll disappear on their own.
That’s not a great idea when the check engine light flashing or blinking. When an engine misfires, fuel can pass into the exhaust system to the catalytic converter. The catalytic converter captures hydrocarbons, carbon monoxide, and nitrogen oxides. It then converts them into harmless compounds. To do this, it operates at extremely high temperatures.
When excessive amounts of fuel make their way to the catalytic converter due to an engine misfire, the fuel can ignite. That can destroy the converter. Typical catalytic converter replacement starts around $1,000 and can quickly surpass $3,000 for some vehicles.
Misfires can also damage fuel cylinders, oxygen sensors, vacuum lines, and other vital components. Play it safe and have your vehicle towed to a certified mechanic.
Why Is My Check Engine Light flashing When Accelerating?
A misfiring engine cannot create enough power to operate your vehicle normally. When you try to accelerate, your engine works harder — and your vehicle’s emissions control system notices the problem.
If your check engine light only blinks when you step on the gas, there’s a good chance that you have an ignition system fault or a temperature sensor issue. Still, you’ll need to read the OBD2 codes to get a definitive diagnosis, and you shouldn’t drive the vehicle until you’ve done so.
What To Do if the Check Engine Light Comes On
If your check engine light comes on and blinks steadily, get your vehicle to a safe place and turn the engine off. Pay close attention to any symptoms that might help a mechanic locate the source of the problem. For example, if you notice a loss of power, excessive vibration, and other indicator lights, make sure your mechanic knows.
If the check engine light is steady or if it flashes intermittently under certain conditions, you can probably drive it to a service station. However, if you notice any signs of a misfire or if your engine is overheating, have it towed.
Any check engine light is a cause for concern, but a blinking CEL indicates a serious problem that could damage your engine. An intermittent indicator that goes off after a few minutes might not be a serious cause for concern but still warrants attention. If your CEL blinks steadily, turn off your engine as soon as you can. Get your vehicle towed to a qualified mechanic. While towing bills can be expensive, they’re nothing compared to the cost of a new engine.
Provided that you’re able to turn off your engine as soon as it starts misfiring, you might avoid a hefty repair bill. Mechanics can fix many engine misfires easily. If you’re fairly handy, you might be able to handle spark plug replacements and other minor issues associated with this symptom. Just be sure to treat the problem seriously — and whatever you do, don’t operate your vehicle until you’ve obtained a proper diagnosis.