Check Engine Light Flashing When Key Is On Position (Explained)

So you just put the key in On position and the check engine light started flashing? If you’re curious about what causes this and whether you should do something about it, read this guide for more information.

Check engine light flashing when the key is On position is usually a “bulb test” to confirm that the check engine light bulb is functioning whenever you turn on the ignition. The light should go off a few seconds after the engine starts running.

Our guide below gives you more details about check engine light flashes on whenever you put the key in the On position. We have also shared more info about when you should be worried about the CEL flashing.

Why check engine light flashes when key is on position

Check engine light flashing when you turn the key in the ON position is perfectly normal and nothing to be worried about. It happens all the time, especially with all the modern, computerized car models.

The light coming on is usually a “bulb check” performed by your car computer to confirm that the CEL is working fine and will alert you when a problem arises as you continue driving your car.

This is an important process since the check engine light bulb may have burned off. And as such, it won’t illuminate whenever the vehicle computer wants to warn you about an issue with your car engine that needs fixing.

Not just the check engine light…all the other system lights on the dashboard will come on when the key is in On position for the same reason—to let you know they’re in good working condition. These include airbags, ABS, traction control, and battery lights.

The ONLY time you should be worried if the CEL flashes when the key is ON position is if the CEL stays on even after the engine has started running. This indicates the car engine has a problem that needs to be diagnosed (more information about this issue coming up later in the post).

Mind you, this is an important part of inspection for anyone looking to buy a used car. Make sure the check engine light as well as all the other system lights on the dashboard come on when the key is in the ON position and go off after firing up the engine.

If this doesn’t happen, then the CEL bulb has most likely been tampered with to hide an issue your car engine is experiencing.

What should you do if the check engine light is flashing with the key on?

You should NOT do anything if the check engine flashes with the key in ON position. Don’t panic. Instead, you should be happy that the CEL has come on upon turning on the ignition.

As we have just said above, this is perfectly normal for all cars and a good sign that your check engine light and all the other engine-related lights are functioning well.

If the light doesn’t come on, that’s when you should be worried because the light bulb isn’t working and you won’t be alerted if your engine develops a problem. This increases the risk of damage to your engine as you won’t fix the problem on time.

The light not coming on briefly could be a sign its bulb has burned out and needs to replace with a new one. This is a cheap fix, so there’s nothing to worry about.

Also, in case you just bought a used car, the CEL not coming on when you turn the ignition should be a reason to worry as it means the bulb has been interfered with.

When you turn the engine on, the light will clear off on its own and you won’t need to use any scanning tool to reset it.

However, if the car computer detects any faults in the engine, the light may stay on after the engine starts running. And this brings us to our next topic below…

What if the check engine light doesn’t go off after you start the engine?

If the check engine light stays on after you have fired up the engine, then you have a problem with your car engine. The light may stay on steadily or in a flashing manner. In either case, we suggest that you go to the repair center to have your car checked for any underlying issues.

Luckily, the trouble codes that have triggered the check engine light will have been logged into the computer memory. All you have to do is use a code reader to pull the codes to help you find out what issue your engine is experiencing.

However, keep in mind that in some car models, the check engine will stay on and disappear shortly after the engine starts running. So you shouldn’t misinterpret the light illuminating for a short while after the engine is running as an engine issue alert.

Otherwise, if the CEL stays on long after the engine has started running, then a diagnostic trouble code has been detected and the light is telling you something out of normal is happening to your car engine.

What if the check engine light doesn’t come on when the key is in on position?

As we have said above, CEL Off when the key is in on position is out of the normal and not a good sign. There are various reasons why this happens. Below, we discuss the most common reason why this happens and possible solutions.

Burned-out CEL bulb

Check engine light bulb doesn’t last forever and will get burned out at some point. if this happens, the bulb will not come on when you turn the key in on position. Here, you just need to replace the old damaged bulb with a new one to get the CEL back up and working again. You can do this on your own or hire a mechanic for the job.

Blown ignition switch fuse

The ignition switch fuse is situated in the battery compartment and can get easily blown if an intolerable electrical charge gets transmitted to the ECU. If this happens, the ECU stops working and the CEL is consequently affected. This should be one of the areas to check if your CEL doesn’t come on.

Damaged ECU (electronic control unit)

ECU is the heart of your car engine and performs all the essential functions. If it’s damaged, the CEL won’t come on when you turn on the key. A damaged ECU also means your car won’t start.

If the engine light fails to turn on and your car fails to start, the ECU may be damaged. In this case, you’ll need to replace the ECU. This is an expensive fix and will most likely be done by the dealership.

Blown ECU fuse

If the fuse for the ECU is blown, the ECU will not be supplied with power, making it unable to do the bulb test when the key is turned on. Just replace the blown fuse and the engine light will start working again.

When should you be worried about the check engine light flashing?

We have just said you have nothing to be worried about if the engine light flashes when you turn on the ignition. So when should a flashing check engine light be a problem?

The simple answer: Any time the check engine starts flashing while the engine is running, you should get worried. A flashing or blinking CEL should scare you more than a steady CEL because it indicates that your engine has a critical problem that requires immediate action.

We recommend against trying to operate your car any further if the CEL is flashing. Just pull it over if it is safe to do so and have a mechanic do a check engine light diagnostic on it. or you can have it towed to the repair center for diagnosis and repair.

The most common causes of a flashing engine light include a loose fuel gas cap, faulty catalytic converter, oxygen sensor issues, fealty air flow sensor, or bad spark plugs.

Some of these causes can mutate into a serious problem and cause catastrophic engine damage. That’s why it’s advisable to NEVER ignore a flashing check engine light!

If you’re experiencing a flashing key on position light, it could be a sign of a serious issue with your car’s engine. However, there are other possible causes you should check before assuming the worst. For instance, a flashing traction control light on or flashing then solid check engine light could also be the culprits. To learn more about these potential causes and what you can do to fix them, check out our articles on flashing traction control light on and flashing then solid check engine light. These articles provide helpful tips and insights on how to troubleshoot and solve these issues, so you can get back on the road with confidence.

Frequently Asked Questions:

Final Verdict

You have nothing to worry about if the check engine flashes when you turn the key in the ON position but do not start the engine. The light is supposed to come on briefly and then go off once the engine starts running. This is a simple bulb check that ensures the CEL bulb as well as other system lights are in good working condition and will alert you in case any problem arises when operating your car.

However, if the check engine light doesn’t go away after the engine starts running, then you should be worried. This is an indication that your car engine is experiencing a problem. You should have a mechanic scan your car computer for the trouble codes that caused the CEL to stay on. This way, you’ll get to know what’s ailing your car engine and fix it on time.