Check Engine Light Flashes On Startup Then Stops: Decode the Message!

In this guide, we’re going to talk about a problem that many of us have experienced: the dreaded Check Engine Light flashing on during startup then stops. Trust me, I’ve been there myself and it can be incredibly frustrating.

There’s nothing worse than getting ready to hit the road and then being met with that ominous warning light.

In this post, I’ll be sharing some of my best tips and suggestions for troubleshooting the cause of a Check Engine Light that flashes on during startup. 

So, why check engine light flashes on startup and then stops? The check engine light flashing briefly at startup indicates the vehicle’s onboard computer is running a self-diagnostic check. If the light stays on or flashes continuously, it signals a problem detected with the engine, emission system, or related components. Have the vehicle inspected immediately by a qualified technician, as intermittent misfires could be occurring. Use an OBDII reader to check for diagnostic trouble codes, which can help identify the issue. Prompt diagnosis is recommended, as engine problems left unattended may worsen.

Bonus Read: Check Engine Light Flashing and Car Shaking

Check OBDII Codes If Check Engine Light Flashing

Even if the check engine light just flashes on a startup (mostly happens on a cold engine startup) and then stops, you should check the trouble codes stored in the engine’s memory using the OBDII scan tool. 

Checking OBDII codes is a relatively simple process. Once you have the scanner, plug it into your car’s OBDII port, which is usually located under the dashboard on the driver’s side. Turn on the scanner, and it will read the code generated by the check engine light. The scanner will provide a description of the code, which can help you to identify the problem. 

There are many cheaper OBDII scanners available. But, I would highly recommend the BlueDriver scan tool. It connects to both Android and iPhone via Bluetooth. It is also packed with a range of features.

checking trouble codes using OBD2 scan tool

The format for engine cylinder misfire codes is typically ‘P030X‘, where ‘X’ indicates the specific cylinder number where the misfire is happening. Therefore, a ‘P0301‘ code signifies that the misfire is occurring in cylinder one.

If you are unsure of how to identify engine cylinders, I have created this guide to help you.

In the event that the trouble code displayed is ‘P0300‘, it indicates that the engine misfire is happening randomly and is not limited to any one cylinder. A deficient oxygen sensor (either lean or rich mixture), vacuum leaks, or a loss of compression could be the source of this issue.

Note: It is a common misconception among car owners that a misfire in a specific cylinder can easily be fixed by simply replacing the spark plug or ignition coil. However, this assumption is not always accurate. Misfires in a vehicle can stem from various underlying factors, from clogged fuel injectors to a blown head gasket, worn-out piston rings, damaged valve spring, or a faulty camshaft solenoid. As such, it is crucial to thoroughly investigate and troubleshoot all possible causes of a misfire in order to accurately pinpoint the root of the problem and effectively resolve it.

Why Does Misfire Occur In Engine?

A misfire can occur in the engine cylinders due to the following potential reasons:

  • Incorrect spark timing: The spark timing is an essential factor in the combustion process. It is the precise moment when the spark plug ignites the fuel mixture in the cylinder. If the spark plug or its wiring is damaged, it will not generate a spark at the right moment. It will also cause a misfire and result in car shaking.
  • Fuel delivery issues due to bad fuel injectors or a bad fuel pressure regulator: Fuel delivery issues are another common cause of engine misfires. The fuel injectors deliver the fuel to the engine, and if they are clogged or malfunctioning, the engine may misfire. The fuel pressure regulator is responsible for maintaining the correct fuel pressure in the fuel system. A faulty fuel pressure regulator can cause the engine to receive either too little or too much fuel, resulting in a misfire.
  • Loss of compression due to a blown head gasket or poor valve timing: Loss of compression can also cause a misfire in an engine. Compression is the pressure that builds up in the combustion chamber when the piston moves up during the compression stroke. A worn or damaged piston ring, cylinder wall, or valve can cause a loss of compression. A blown head gasket can also cause a loss of compression.

Causes Of Check Engine Light Flashing On Engine Startup

Here are the causes of the check engine light flashing on startup:

1. Intermittent Misfire When The Engine Is Cold

Most people, who have encountered the problem of a flashing check engine light on startup, have experienced intermittent engine misfires when the engine is cold. This is also called a cold engine startup.

When you start the engine after a long time (even after 8 to 12 hours), the chances are that your vehicle will start shaking and idling rough due to engine misfire and the check engine light will also start flashing but might stop after a while.

In those cases, vehicle owners have also reported that after restarting the engine right away, the check engine light goes away and the engine starts running normally.

On the engine startup after a long time, the misfire usually happens till the engine reaches its operating temperature.

Why does it happen?

The reason why misfires can happen and check engine light flashes on a cold engine startup is that in gasoline engines, there is a direct injection of fuel through fuel injectors. The fuel only burns in a certain range of temperature.

At cold engine temperature, it also narrows down the range of the burning temperature of the fuel. As a result, it will make it hard for the fuel to burn uniformly with the air.

As a result, the vehicle experiences a misfire on a cold engine startup and the check engine light starts flashing but goes away as the vehicle warms up.

How to prevent?

Using the right oil can make a big difference in preventing cold engine misfires on startup. Make sure to use the oil recommended by your car’s manufacturer, as it has the right viscosity and additives to keep your engine running smoothly in cold temperatures. 

You can read my guide on SAE 30 vs 10W30 oil to learn more. You can also read my guide on the best oil for high-mileage engines.

Letting your engine warm up for a few minutes before driving can help prevent cold engine misfires on startup. This gives the oil a chance to circulate and the engine to reach its optimal operating temperature and the catalytic converter to reach its operating temperature.

The quality of your fuel can have a significant impact on the performance of your engine.

Low-quality fuel can cause a number of problems, including cold engine misfires. This is because low-quality fuel may contain impurities or contaminants that can clog your fuel injectors or cause your spark plugs to malfunction.  

2. Bad Camshaft Solenoid

bad camshaft solenoid

A camshaft solenoid is a small electric valve that controls the flow of oil to the camshaft. It is located in the engine block and is connected to the engine’s computer system. The solenoid is responsible for regulating the oil pressure that reaches the camshaft, which in turn controls the engine’s valve timing. 

The camshaft is connected to the cam phaser. The engine oil flow through the cam phaser is controlled by the camshaft solenoid.

If the solenoid is clogged with carbon and gunk of oil, the oil flow will not be monitored. As a result, the valve timing of an engine will disturb. Due to this reason, your car shakes and the check engine light starts flashing for a few seconds on engine startup.

To learn more about the cam phaser, camshaft solenoid, and valve timing, you can read my guide on how cam phaser goes bad.

Why does it happen?

So, basically, when the engine is cold, the oil is thicker and more viscous, which can cause the solenoid to become clogged with debris. This can prevent oil from flowing to the camshaft, causing it to malfunction and resulting in a cold engine misfire on startup. 

When the camshaft solenoid fails, it can cause a lack of oil pressure in the engine, resulting in poor lubrication.

This lack of lubrication can cause the engine’s camshaft to stick, leading to a cold misfire. The misfire occurs because the camshaft is not functioning correctly, which leads to an imbalance in the engine’s cylinders.

The camshaft solenoid’s failure can also cause the engine’s computer to misinterpret the data from the camshaft position sensor. This misinterpretation can cause the engine to misfire and run poorly, especially during a cold startup.

When the engine becomes warm and reaches its operating temperature, the oil has a better flow and easily passes through the camshaft solenoid. Due to this reason, the misfire goes away after a few seconds.

How to fix it?

You have to test the solenoid when the engine is cold. Follow the below video for a better understanding:

3. Carbon Buildup On The Back Of the Intake Valve

carbon buildup on air intake in GDI engines

GDI engines are designed to inject fuel directly into the combustion chamber, rather than into the intake manifold like traditional port fuel injection engines. This design allows for better fuel economy, increased power output, and reduced emissions. However, it also creates an environment in which carbon buildup can occur.

When gasoline is injected directly into the combustion chamber, there is no fuel passing over the back of the intake valves to clean them.

As a result, over time, carbon deposits can accumulate on the back of the valves. This buildup can restrict airflow into the engine, leading to decreased performance, reduced fuel economy, and increased emissions.

Carbon buildup on the back of the intake valve can cause several issues for the engine. One of the most common problems is cold misfires.

When the engine is cold, the carbon buildup can prevent the intake valve from closing properly, allowing some of the air/fuel mixture to escape back into the intake manifold. This can cause a misfire, which is typically felt as a rough idle or hesitation when accelerating from a stop.

In addition to cold misfires, carbon buildup on the back of the intake valve can also cause the check engine light to flash.

This is because misfires can cause damage to the catalytic converter, which can lead to increased emissions.

Once the engine warms up and the carbon on the back of the intake valve begins to burn off, the misfires and flashing check engine light typically go away.

Why does it happen?

When GDI engines were introduced, API standards for engine oils were upgraded to API SP. So, if you have been using an engine oil that is not API SP certified, it can cause carbon buildup issues. On the bottle/tin of the engine oil, the API SP certification label should be stamped.

Moreover, if there is a crack in the valve stem seal (the arm of the valve is called the valve stem), the engine oil will leak through it and deposit on the back of the valve.

Moreover, when the engine is cold, piston rings shrink a bit. The unburnt fuel vapors leak through it and accumulate in the crankcase (the place where engine oil settles).

From the crankcase, these gases route through the PCV valve and enter the engine cylinder via the air intake manifold. Most of the gases burn but some of them cake up on the valve stem.

Since in GDI engines, no gasoline flows through the air intake port, carbon will start building up.

How to fix?

Use correct viscosity grade oil and the oil meets the standards recommended by the API. Moreover, make sure that PCV (Positive crankcase ventilation) valve is not stuck open.

If the PCV valve is stuck open, excessive unburnt hydrocarbons will enter air intake manifold and produce a large chunk of carbon buildup.

Moreover, in engines, there is an air oil separator (AOS). If it has any crack, air will also carry vapors of oil with it and enter the engine. It will also cause engine misfires for a few seconds.

3. Clogged Fuel Injectors

clogged fuel injectors

Fuel injectors are responsible for delivering fuel to the engine’s combustion chamber. They work by spraying a fine mist of fuel into the engine’s intake manifold, where it mixes with air and is then drawn into the combustion chamber.

In modern engines, fuel injectors are controlled by the engine’s computer, which determines when and how much fuel to inject based on a variety of sensor inputs.

Over time, fuel injectors can become clogged with dirt, debris, and other contaminants. This is especially true if you regularly use low-quality fuel, as these fuels often contain high levels of impurities.

When fuel injectors become clogged, they may not be able to deliver the proper amount of fuel to the engine’s combustion chamber. This can cause the engine to run lean, which means there is too much air and not enough fuel in the combustion chamber.

A lean fuel mixture can cause a misfire, which is when the air/fuel mixture in the combustion chamber fails to ignite properly. When this happens, the engine may run rough, shake, and emit a strong smell of unburned fuel. Additionally, a misfire can cause the check engine light to flash. 

When the engine starts and it is cold, the fuel could not be injected by a clogged fuel injector in a suitable way, which could cause a flashing check engine light. 

After a few seconds, as the engine warms up and the fuel injector continues its operation, the accumulated dirt and debris might get washed away and the misfire could go away.

How to spot the cause?

To learn how to inspect fuel injectors, you can reads my guide on car won’t start after replacing fuel injectors.

Final Thoughts

In summary, a check engine light flashing briefly on cold startup is often due to transient issues like fuel injector clogs, camshaft solenoid blockages, or carbon buildup on valves which resolve as the engine warms up.

Thorough diagnosis using OBD codes is key to pinpointing the root cause. To prevent reoccurrence, use quality gas, API-certified oil, address leaks, and regularly clean intake valves.

With proactive maintenance and prompt diagnosis, flashing CELs on startup can be preempted. The light indicates an adaptive system responding to changing conditions – understanding the adaptive nature provides wisdom to resolve causes.

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