No Check Engine Light When Key Is In On Position [Fixed]

Are you facing the issue of no check engine light when key is in on position? This problem is generally caused by a blown ignition switch fuse, burned-out bulb, faulty oxygen sensor, blown ECU fuse, and damaged ECU.

Keep reading this article to find out more about these issues in detail. We’ll also discuss how you should go about solving each of these problems.

No Check Engine Light When Key Is In On Position [Fixed]

We’ll look at the most common reasons why the check engine light doesn’t come on when the key is turned on in this section. Some problems are easy to fix while others require you to visit the mechanic.

It’s best to have a professional mechanic inspect the engine lights if you run into this problem. He’ll diagnose the problem by connecting a scanner and reading the ECU codes.

Different codes reflect different problems. The mechanic will know what to do in each case and fix the issue. With that said, let’s check out the typical reasons that cause the check engine light to turn on.

Note: You can also read how to fix Engine Light On After Oil Change.

1. Blown Ignition Switch Fuse

There’s a fuse in the battery compartment of your car which is called the ignition switch fuse. This fuse gets blown if an intolerable electrical charge is sent to the ECU.

The ECU will stop working and will cause the check engine light not to come on. This is the first thing you should check before you purchase the other expensive components that could also cause this problem.


The fuse needs to be replaced if this is the problem. The ignition switch fuse is very cheap and easy to replace. You just have to take the old fuse out and replace it with a new one.

2. Burned Out Bulb

It’s common for check engine light bulbs to get damaged with time. Everything is fine with your car if this is the issue. But the bulb that lights up the check engine light is damaged and that’s why it won’t turn on.


The bulb has to be replaced. Replacing the bulb by itself is an easy job for everyone. But the problem is that you have to pull out the radio and dashboard first to access the information cluster.

Whether you want to replace the bulb yourself or hire a mechanic is up to you. Go with a mechanic if you’re unsure about putting the parts back together without damaging anything.

3. Faulty Oxygen Sensor

Many sensors are connected to the ECU. These sensors include Fuel Pressure sensors, Battery Current sensors, Oxygen sensors, etc. The check engine light won’t work if any of these sensors fail.

The oxygen sensor has a higher tendency to fail than the other sensors and it could be causing the problem.


Replacing the faulty oxygen sensor should fix the issue. You’d have to take the car to a mechanic or get a scanner yourself to know which one of the sensors is causing the issue.

Most oxygen sensors are screwed to the exhaustion system. Disconnect the electrical wire that is connected to the sensor. Unscrew the old sensor and put the new one in its place.

4. Blown ECU Fuse

If the ECU fuse is blown, the ECU will not get power and the check engine light won’t turn on. The wiring also gets loose between the connectors which can also cause the problem.


You need to replace the ECU fuse to get the check engine light working again. Make sure that your battery is fully charged when you check if it’s working. 

5. Damaged ECU

The ECU is a vital part of your engine that performs essential functions. If it becomes damaged, the check engine light will not come on. You won’t be able to drive your vehicle properly either with a damaged ECU.

If the check engine light doesn’t turn on and the car fails to start, you could be looking at a damaged ECU.


Replacing the ECU is the only solution in this case. Unfortunately, it’s expensive to replace the ECU but you have no other option if you want your engine to work well.

How Do I Reset My Check Engine Light Manually?

Follow these steps to reset your check engine light:

  • Turn off your car’s engine and pop the hood.
  • Locate the car battery and find the negative battery terminal.
  • The red one is the positive battery terminal and the black one is the negative one.
  • Disconnect the negative battery terminal and leave it for a minute or two.
  • Connect it again and your check engine light should be fixed.

This is only a temporary solution if you haven’t fixed the underlying problem that is causing the check engine light to turn on. You have to fix the issue that turns the check engine light on. You can’t get around that.


Is the check engine light supposed to come on when you turn the key on?

Yes, all the lights on your information cluster will light up to let you know that they’re working properly. The check engine light will turn off if your car is fine.

Why does my engine light stay on even after I turn off my car?

The ECU may take a little longer to shut off after you turn off the car. If the light is on after turning off the engine, there’s something wrong with your vehicle and you must get it checked.

Can you disable a check engine light?

You can disable the check engine light by taking off the bulb from the information cluster. But the CEL is there for good reason and you should never disable it.

What does the ECU do?

The Engine Control Unit or ECU is the brain of your engine. It maintains the right ratio of fuel and air in your engine so that it runs properly. It also alerts you if there’s any problem with your car. 


Now you know what causes no check engine light when key is in on position in a car. It’s best to have a professional mechanic read the error codes to determine the problem before you go out shopping for parts.

We hope the tips we shared will help you figure out what’s causing the problem with your check engine light and how you can fix it. Leave a comment below if you have any questions!

About John M

John contributed as a technical head at an automobile company just 2 years after his post-graduation in Automobile Engineering. He loves to lead a free life, so he left his job & started blogging. Now, he does research on every automotive problem, part & product and seeks a better solution & best products & shares his findings with his readers to help them as well as to minimize their struggle.

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