Check Engine Light Flashing When Key Is On Position: Here’s What To Do

Every driver knows the sudden anxiety that washes over them when they spot the Check Engine Light on their dashboard. It’s akin to the vehicle’s heartbeat, and a crucial indicator of its overall health. It’s your car’s way of communicating that something may be amiss and requires your attention.

While a steady light might give you a moment to breathe and schedule a mechanic’s visit, a flashing one is more like your car screaming, “Emergency!”

How about situations where you notice this check engine light flashing when key is on position?

I’ve seen some car owners get worried over the illumination of the check engine light when they turn the key to the “on” position. If this situation resonates with you or you are facing similar issues, this article is for you.

I know you are wondering why your Check Engine Light would decide to flash when the key’s turned to the “on” position, but the engine’s not running. You’re right to be cautious, though. Let’s shed some light on this puzzling issue.

check engine light flashing when the key is on position

Why Does the Check Engine Light Flash When the Key is in the “On” Position?

I know you get a mini heart attack when you see your Check Engine Light flashing the moment you turn your key to the “on” position. However, take a deep breath; it’s usually not as bad as it seems.

This brief flashing episode is known as a “bulb check.” It’s like your car giving itself a quick physical exam before it gets moving.

When you insert the key and turn it to the “on” position, the car’s computer quickly takes inventory of essential systems, including the Check Engine Light.

This check ensures that the bulb is functional and capable of alerting you should there be any engine issues.

Imagine you’re driving down the road and you’re completely oblivious to a problem with your car because the Check Engine Light bulb burned out.

That’s why this bulb check is crucial. It confirms that the warning systems are operational, setting the stage for more accurate diagnostics if an actual issue arises while driving.

And it’s not just the Check Engine Light that goes through this self-assessment; other important warning lights like the airbag, oil, and battery lights will do the same thing.

In essence, your car’s just doing its due diligence, ensuring it can communicate with you effectively if something goes wrong.

What Should You Do if The Check Engine Light is Flashing when the Key is in Position?

If your Check Engine Light flashes for a moment when you turn your key to the “on” position, you don’t need to do anything. It’s like a thumbs-up from your vehicle before you hit the road.

It might sound counterintuitive, but in this scenario, a flashing light is a good sign. Your car’s basically giving you a green light; well, a flashing orange one, to continue with your journey.

If you find that the Check Engine Light doesn’t come on at all when you’re doing that initial system check, that’s when you should be concerned.

A bulb that doesn’t illuminate could mean you’ll be in the dark if a real issue occurs while driving. In such cases, you’d want to get that fixed right away. Otherwise, you could be blissfully unaware of problems that, if left unaddressed, could lead to more serious and costly repairs.

Other Things You Can Do if Your Check Engine Light is Flashing When Key is on Position

A flashing Check Engine Light usually indicates a more serious issue than a steady light. If the light only flashes briefly and then turns solid, it may be running a system self-check. If it continues to flash, there’s likely a more serious problem.

Consult your vehicle’s owner’s manual as it could have specific information on what a flashing Check Engine Light means for your make and model, including any steps you should take immediately.

If your Check Engine Light is flashing continuously after the key is in the ‘on’ position, I would generally advise that you do not drive the vehicle and seek immediate service, as driving could cause further damage to the vehicle.

Automotive issues can be complex and often require specialized diagnostic tools like OBD Scanners and knowledge to identify and address the issues properly. It’s usually a good idea to consult with a qualified mechanic for an accurate diagnosis and appropriate repairs to your car.

What if The Check Engine Light Doesn’t Go Off After You Start The Engine?

Now, here’s where things get a tad more serious. If your Check Engine Light stays lit or continues flashing even after your engine is up and running, then that is a problem.

Reasons Why the Light Might Stay On

  • Engine Misfires: Your engine could be misfiring, which means that one or more cylinders aren’t firing correctly. This could be due to spark plugs, fuel delivery, or a variety of other factors.
  • Oxygen or Mass Airflow Sensor Failures: Modern cars are filled with a range of sensors, like the oxygen sensor, mass airflow sensor, and more, that could fail and trigger the Check Engine Light.
  • Emissions System Problems: If your car’s emissions system isn’t working correctly, it could trigger the light to stay on.
  • A Failing Catalytic Converter: In the worst-case scenario, a continuous Check Engine Light could indicate a serious issue like a bad catalytic converter, which could lead to more severe damage if not addressed promptly.

Immediate Actions to Take If the Check Engine Light Stays On

  1. Do Not Drive the Vehicle: I know you might think driving to the nearest repair shop is a good idea, but trust me, it’s not. You could worsen the issue and end up with a much higher repair bill.
  2. Disconnect the Battery If Safe: This is something to approach with caution. If you’re comfortable and know what you’re doing, disconnecting the battery could reset the car’s computer and possibly turn off the Check Engine Light. But this is a temporary solution and doesn’t address the underlying issue.
  3. Seek Professional Help Immediately: Sadly, this is not the time for DIY fixes. Call your trusted mechanic or tow your car for a thorough diagnostic. It is better to be safe than sorry.

Common Check Engine Light DTCs and their Meanings

When that Check Engine Light comes on and stays on, your car’s computer often stores a Diagnostic Trouble Code (DTC) to tell you and your mechanics what’s going wrong. Below are some common DTCs you might encounter when dealing with a Check Engine Light situation.

1. P0300: Random/Multiple Cylinder Misfire Detected

This P0300 code suggests that one or more cylinders are misfiring in your engine. Misfires can lead to higher emissions, poor fuel economy, and reduced engine performance.

Simply put, if you see this code, your engine’s not running as smoothly as it should be, and it’s time to get it checked.

2. P0420: Catalyst System Efficiency Below Threshold

In non-mechanic speak, the P0420 code usually means your catalytic converter isn’t doing its job efficiently. The catalytic converter helps reduce harmful emissions released into the atmosphere. It can reduce your car’s performance and fuel efficiency when it’s not working properly.


It is important to understand why the Check Engine Light might flash when you turn the key to the “on” position and what you should do if it doesn’t turn off once the engine is running.

While that flashing light during the initial system check is typically nothing to worry about, a light that remains on after your engine starts is your car’s urgent way of telling you something’s not right.

While you may feel tempted to ignore the light, the safest action is to consult a professional mechanic. Your mechanic has tools, like the OBD Scanner, and enough expertise to properly diagnose and resolve whatever issue is causing that stubborn Check Engine Light to stay on.

So, don’t hesitate to seek your mechanic’s help when you are in doubt.