What Does the ‘Check Engine Light’ Mean?

By Angela Monroe - September 9, 2020

What Does the ‘Check Engine Light’ Mean

PANIC! Is usually the first thing drivers think when they see the check engine light. This is often followed by fears of extreme wallet damage. But what does it mean for your car and what are you supposed to actually check?

We investigate the perceived ‘icon of death’: the check engine light.

What are you supposed to check?

man sitting on car bonnet

When the check engine light comes on, it doesn’t really mean you need to pop the hood and look at the engine. Modern cars have countless sensors which monitor things like exhaust temperature, oil pressure and temperature, air/fuel mix, oxygen, camshaft, wheel speed… in other words, a whole lot of stuff.

Depending on make, model and year of manufacturer, the check engine light means connecting your car to a diagnostic tool to see what fault codes it displays.

A what tool?

A diagnostic tool is a handheld device that, depending on the vehicle, plugs into a port located under the dashboard. The device will display error codes on a screen. It allows the user to quickly see the problem with the car first indicated by the check engine light. 

What are these ‘codes’?

As modern engines are extremely complicated, it takes a professional to understand and correctly repair the fault. An example of a fault code is: “P0131”. Not much help to your average motorist. This means a sensor problem but do you replace the actual sensor causing the code or is it a side effect of something more serious?

Did You Know? In 1996, automakers began to standardise their fault codes in a universal language. This language is called OBD-II.

Common reasons for a check engine light:

Woman looking at codes

There are hundreds, if not thousands of reasons why the check engine light can come on. However, some reasons are more common than others. Note that the codes aren’t ‘black and white’, they can mean a side effect or part of a large problem. Here are some of the most common:

1: Faulty oxygen sensor

The O2 sensor is tasked with measuring oxygen in the exhaust to allow the engine control unit to adjust the air / fuel ratio correctly.

OBD-II code: P0420

2: Mass airflow sensor fault

This guy’s job is to measure the air coming into the engine. They are found behind or after your car’s air filter. Like the oxygen sensor above, they play a role in the air/fuel mixture. 

OBD-II code: P0101

3: Loose petrol cap

Easy to fix, but obviously dangerous. This fault can result in incorrect pressure in the tank and debris like dust or even rainwater getting into the fuel. 

OBD-II code: P0440 (this can also indicate a fuel leak)

4: Spark plug/ignition coil issues

This indicates a problem with your car’s spark it generates to ignite the fuel in the cylinders. It might mean replacing your spark plugs or something or an electrical fault.

OBD-II code: P2335

5: Vacuum leak

Cars have vacuum systems that perform numerous functions. The brake booster and harmful emissions control are examples. These problems are usually cheap to replace but expensive to locate as cars have a lot of vacuum hoses.

OBD-II code: P2279 

What should you do if your car’s check engine light comes on?

mechanic looking at suspension

If your car displays the check engine light, your best bet is to drive it gently and carefully to a professional mechanic to be correctly diagnosed. Checking the basics like your fuel cap, any visible smoke from the exhaust or loose connections in the engine bay are a good idea too.

A more serious consequence of the check engine light is the infamous ‘limp home mode’.

‘Limp home mode’ means the car is in a safety mode to reduce more damage. Less important things like air conditioning will often turn off the car will significantly reduce the speed and power of the engine. 

Seek professional advice as soon as your check engine light comes on.

Looking at buying a used car? Test drive it like a pro and make sure the check engine light isn’t on.

End of the Day

woman driving and smiling

If you give your car a regular spring clean and know the red flags, you’ll know what to look out for and avoid serious damage and seriously expensive repair costs. Like with most things, the better you take care of it, the less risk of problems you’ll have.

Angela Monroe
Angela Monroe is the Community Manager at The Positive Group, specialising in giving people the information that they need when they need it, and putting you on the path to a fair financial future. She has 8 years of experience in helping Australians find the right finance solutions, and regularly contributes articles to empower Australians with the knowledge they need to become financially healthy.


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