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Car Care Advice

What to Do When Your Check Engine Light Comes On (+6 Causes)

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You’re driving along, minding your business, when a light pops up on your dashboard. It looks like the outline of a car’s engine, along with the words “check engine” or “service engine soon.” 

That’s called the check engine light— something you don’t want to see while driving.

So, why is it on, and should you be concerned?

Don’t worry!
In this article, we’ll explain all you need to know about the check engine light— what it means, how to fix it, and also go through some related FAQs.

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Let’s get started.

What Does a Check Engine Light Mean?

The check engine light, or malfunction indicator light, usually means that your car is experiencing an engine problem. But it can come on for many other reasons, ranging from a simple loose gas cap to a more serious bad catalytic converter.

Furthermore, what triggers the light varies by year, make, and car model.

In other words: There’s no way to say exactly why the engine light is on without performing diagnostic work.

So how do you know when you have an emergency?
You can judge how serious an issue is by looking at the warning light. The check engine light can show up in two ways:

The bottom line is you should always get your vehicle diagnosed and repaired regardless if it’s a solid or flashing check engine light.

So how do you deal with a lit check engine light?

What to Do When the Check Engine Light Comes On 

If your check engine light suddenly comes on while driving, here are some tips:

  1. Remain calm and pay attention to how the car feels. For example, note if the engine feels weak or sluggish and if there are any weird noises. Sometimes, your car immediately enters a “limp mode,” where the module automatically turns off some minor accessories and restricts your speed. This way, the engine produces less power and helps prevent further damage.
  1. Drive slowly and get driving directions to the closest service center or auto repair expert. Also, keep an eye on your dashboard gauges to check if you’re running out of fuel or overheating. 
  1. If you have a flashing check engine light, try to find a safe place to stop. Don’t rush, as you want to avoid adding stress to the engine. Once you’ve parked your vehicle, turn off the engine. Immediately schedule a check engine light service, or better yet, get a mobile mechanic to come to your aid. 

Knowing what to do when the check engine service light comes on can save you from costly repairs. 

But what causes an illuminated engine light in the first place?

6 Reasons Why Your Check Engine Light Might Be On

Your engine light comes on for several reasons, from bad spark plug wires and a broken gas cap to a faulty oxygen sensor. That’s why you’ll need an auto repair professional to diagnose your car correctly.

Let’s take a closer look at some common culprits behind your lit check engine light.

1. Engine Problems 

An engine problem can trigger the engine light. Most of these problems are related to poor fuel economy. Some examples:

2. Transmission Problems

Your car’s transmission manipulates engine power and transfers it to the drive wheels. Since the transmission and engine work together closely, a transmission problem (like a slipping transmission) can cause poor fuel efficiency.

Therefore, if the control module detects a problem with the transmission, it’ll activate the service engine light.

3. Faulty Emissions Equipment

Modern vehicles have many emissions equipment onboard, like the exhaust gas recirculation system, the catalytic converter, and the evaporative emissions system. These parts help minimize tailpipe emissions and increase fuel economy.

Simple issues like a loose gas cap or fuel cap can trigger your vehicle’s engine light. A faulty gas cap will cause fuel vapors to escape the fuel tank, resulting in poor fuel economy. 

Apart from a broken gas cap, a faulty canister purge valve can also cause fuel vapors to escape the tank and turn on the check engine light.

4. Ignition System Problems 

The ignition system includes everything needed to ignite the air-fuel mixture inside the engine. Problems like a worn ignition coil or bad spark plug wires trigger the engine light. 

A faulty spark plug prevents your engine from starting or causes it to shut off suddenly. If left unattended, you can end up with an engine misfire.

5. Faulty Modules and Sensors

Your engine control unit (ECU) utilizes multiple sensors. Issues with sensors, like a loose oxygen sensor wiring, a clogged-up mass airflow sensor, or a faulty oxygen sensor, can cause the check engine light to come on. 

For example, the oxygen sensor measures the amount of unburned oxygen in your exhaust and informs your ECU, which uses this data to adjust the air-fuel ratio. A faulty O2 sensor may cause your engine to burn more fuel than required, resulting in poor fuel economy. 

6. Overheating

If the engine coolant hasn’t been changed in a while, it can degrade the engine thermostat and lead to overheating. In such cases, your check engine light will turn on, and the temperature gauge on your dashboard will rise. 

When this happens, stop driving immediately. The error code P0217 may accompany the service light.

The average car insurance doesn’t cover all vehicle repairs, so it’s better to schedule service immediately with an auto repair professional to diagnose the issue. 

Let’s see how it’s done.

Diagnosing a Check Engine Light

When the check engine light comes on, your car’s computer stores the corresponding diagnostic trouble code (DTC) in its memory. It can be hard to figure out what a check engine light means, so it’s best to take your car to a service center than to DIY it.

Your mechanic will connect an OBD scanning tool to retrieve the error code.

They’ll use the engine codes as a starting point to troubleshoot and conduct additional diagnostic tests to determine the issue. 

For instance, the trouble code P0300 indicates an engine misfire in more than one cylinder. Your mechanic must conduct further inspections to verify the codes and fix them. Typical causes for such codes are faulty spark plug wires, a bad O2 sensor, a broken mass airflow sensor, or a defective catalytic converter.

Once the issue is resolved, the engine check light should automatically turn off

Typical Repairs for a Check Engine Light

Since there are plenty of reasons why the engine light can come on, here are some possible repairs and their costs:

A check engine light service can get pricey, so it’s best to get car insurance that covers everything, like the AutoNation Protection Plans. 

Now that you know how a mechanic diagnoses a lit engine light, time to answer some FAQs!

3 FAQs About the Check Engine Light

Here are some commonly asked questions about the check engine light.

1. Is Driving With an Illuminated Check Engine Light Safe?

The safest answer is NO. 
You can’t identify what’s causing the activated engine light, so it’s better not to drive when the light is on. 

If you really need to, keep the following car care tips in mind:

You don’t want to strain the engine and cause further damage while getting to the service center.

2. Can Low Oil Cause the Check Engine Light to Come On?

Being low on oil is a serious problem, but it won’t trigger your check engine light. Instead, it’ll activate the oil light. 

However, low oil pressure can switch on the engine light.

Here are some car care tips to prevent it from happening: 

3. Can I Take an Emissions Test With an Illuminated Check Engine Light?

The short answer is no.

Not only are you endangering yourself when you head towards the test site, they may give you an automatic fail if your check engine light is on.

Final Thoughts

An illuminated check engine light isn’t something you should shrug off. It can represent serious issues and engine codes that need immediate attention.

Better than putting it off, why not contact a mobile mechanic like RepairSmith so you can get it checked immediately?

RepairSmith is a mobile auto repair and maintenance service that offers a wide range of repair and replacement services at the tip of your fingers. Our service hours cover seven days a week.

So, why not schedule service with us if you need a check engine light diagnosis, and we’ll send our experts to your location!