When a check engine light starts flashing and the car won’t accelerate. This is the ECU indicating that something is critically wrong with the engine. Often, a flashing check engine light is the result of engine misfire caused by unburned fuel making its way into the exhaust system. This raises the temperature of the catalytic converter which can catch fire. It’s wise to pull over and turn off your car immediately to prevent further damage. Ignoring a flashing check engine light will eventually lead to more serious (read: expensive) problems. Here are fifteen reasons why the check engine light is flashing, and your car won’t accelerate.
1. Improper Fuel Mixture
In modern cars the engine control unit (ECU) limits engine power to prevent further damage any time the check engine light comes on – this is known as limp mode. An engine requires the perfect mix of fuel and air to run smoothly, which is regulated by the ECU. But if the engine can’t get enough air to match the amount of fuel injected into the pistons. What you get is an imbalance of the air-to-fuel ratio causing the engine to run too rich and resulting in a misfire.
2. A Faulty ECU
The ECU is responsible for engine performance. It processes all the information from various sensors throughout your car to adjust the air-to-fuel mixture. As such it controls fuel consumption and spark timing (the order in which spark plugs fire). But if the ECU becomes somehow corrupted, it can affect the firing order of the spark plugs and/or how much fuel is sent to the engine which will cause your check engine light to flash and acceleration can be underpowered.
3. Bad Oxygen Sensor
I can tell you from firsthand experience that a bad oxygen sensor can absolutely cause your check engine light to flash and stop your car from accelerating. This happened to my Nissan Maxima in college. It doesn’t seem like a big deal initially, which is why I kept putting it off. But the longer you put off addressing it. Eventually you’ll experience engine misfires, poor acceleration and rough idling. Also known as an 02 sensor, this small component is responsible for measuring how much unburned oxygen is in the exhaust.
4. Low Compression
When the spark plugs can’t fire in their due sequence either because of too much fuel or improper timing of the spark plugs, the result is low compression. The fuel injector sprays gasoline into the cylinder heads where it mixes with oxygen. Electricity created by the ignition system is sent to the spark plugs. This ignites the fuel and air to create combustion. Low compression can cause misfires and poor performance in the form of a flashing check engine light and poor acceleration. If you have no compression, your car won’t even start.
5. Poor Ignition (Spark) Timing
A misfire can start out as a nuisance like a check engine that won’t stop flashing, followed by diminished acceleration. And can quickly turn into a car that won’t start. Or you could be in the middle of the freeway and suddenly find yourself with no engine power. Ignition timing is essential to engine performance. It determines when the spark plug fires during a compression stroke. A compression stroke is when the piston goes up. Other signs of poor ignition timing are overheating, decreased fuel economy and engine knock.
6. Problems with Ignition (Spark) Coils
Ignition coils amplify your battery’s low voltage into the thousands of volts needed to create electricity in the spark plugs to ignite the air-to-fuel mix. But if an ignition coil malfunctions, it can cause a misfire which will cause your check engine light to flash, and you may not be able to accelerate. A bad ignition coil will cause one of the cylinders in your engine to fire incorrectly or not at all. Ignition coils typically last 80,000 to 100,000 miles.
7. Spark Plug Issues
An engine misfire can be caused by bad spark plugs. A bad spark plug can be the result of carbon buildup, oil in the combustion chamber, overheating, and an improper spark plug gap. There are also many things that can cause spark plugs to go bad like a dirty air filter, excessive driving at low speeds, an air-to-fuel mixture that’s too rich, dirty fuel injectors or leaving your vehicle idling for too long. A misfire means that one or more of the pistons in the engine isn’t producing the power that it should. When this happens the motor has to work harder causing a flashing check engine light and a car that won’t accelerate.
8. Sticky Fuel Injectors
If the misfiring is due to dirty fuel injectors, you’ll feel vibrations throughout the car coming from engine sputter. A fuel injector atomizes and injects fuel into the engine. Bad fuel injectors mess up the delicate balance between air and fuel resulting in too much or too little fuel sprayed into the cylinders. How do fuel injectors become sticky? When excess oil breaks down, it leaves a sticky residue on the injectors – your mechanic may refer to this as stiction. A clogged or otherwise faulty injector can also cause misfires.
9. Weak Fuel Pump
A weak fuel pump that can’t deliver adequate pressure can cause an engine to run lean, misfire and hesitate when accelerating. For a fuel-injected engine to run the way it should, the fuel pump must be able to generate enough pressure to meet the engine’s operating requirements. The fuel pump is the heart of the fuel system. In modern vehicles, you can find it inside the fuel tank. The fuel pump is responsible for delivering fuel from the tank to the fuel injectors so that it can be sprayed into the combustion chamber.
10. Loose Fuel Cap
Like most systems in a car, the fuel system is a closed system. The component that helps maintain that pressure is the fuel cap. And like the radiator cap, it’s one of the areas of a car that’s least thought about – it’s just expected to work. But something as simple as a loose fuel cap can trigger a flashing engine light, leading to wide system problems. There are many reasons why a fuel cap can become loose. The most obvious one comes from the common act of filling your car with gas.
11. Malfunctioning MAF Sensor
Simply having a dirty MAF sensor can cause a lean engine code that causes your engine to misfire. Along the same lines as an oxygen sensor, a mass air flow (MAF) sensor measures the amount of air flowing into a fuel injected engine. As air, dirt and other debris contaminate the sensor, it won’t be able to read how much air is coming in through the intake. The result is the same as a bad oxygen sensor: misfires, poor acceleration and rough idling.
12. A Vacuum Leak
Vacuum leaks confined to one cylinder eventually will cause an engine to misfire leading to unresponsive acceleration and a flashing check engine light. This type of vacuum leak allows additional air into the affected cylinder throwing off the delicate balance of the air-to-fuel ratio, thereby causing a lean mixture. If nothing else, you’ll experience rough idling.
13. Dirty Throttle Body
A dirty throttle body can also disrupt the engine’s air-to-fuel mixture resulting in misfiring, a flashing check engine light and a car that won’t accelerate. In short, a throttle body is made of a slightly oval-shaped plate mounted on a shaft. This plate-on-shaft is sometimes called a butterfly valve. When you press the accelerator the butterfly valve opens allowing more air into the engine so you go faster. Taking your foot off the accelerator closes the valve, decreasing your speed. A throttle body gives you immediate control over how an engine breathes by changing the angle of the butterfly valve.
14. Damaged Head Gasket
A head gasket that’s cracked between cylinders will cause the engine to misfire. This is because a head gasket that’s damaged in this way causes compression from one cylinder to leak into another. A head gasket provides a seal between the engine block and cylinder heads. But a compromised head gasket causes lowered compression. And lowered compression will result in rough idling and misfires.
15. Catalytic Converter Issues
Engine misfires are a sure-fire sign of a bad or failing catalytic converter. A misfire indicates incomplete combustion within a cylinder. This can very well be because the catalytic converter isn’t functioning effectively. This is why if you ever encounter your check engine light flashing, the best thing to do is pull over immediately and turn off the engine. Then, get your car towed to a service station you trust where a trained mechanic can run diagnostic tests to find out exactly why the check engine light is flashing.