Why Does the Check Engine Light Come On? 5 Reasons to Know

The mere sight of that light is enough to make you panic and pull over to the side of the road. After all, it indicates that something is wrong – and we’re all taught from a young age that “something is wrong” with your car means “you’re about to break down on the highway.”

The warning pops up for a reason; it warns you that there’s an issue with your car’s performance. Perhaps there’s a problem in the emission system, or something is wrong with how the engine is running. The light hardwires into your car’s circuitry and then sends messages to display what’s wrong.

So, what could cause the engine light to turn on? The car’s powertrain control module (PCM) reads and decodes diagnostic trouble codes (DTC) from onboard sensors that control the engine, transmission, and other systems. Whenever a fault is detected, such as a misfire in one of the cylinders of your engine, the PCM illuminates a related warning on your dashboard.

Contrary to what you may think, the gas cap is just one of several reasons that your Check Engine Light could be flickering or staying lit. There are actually dozens of separate fault codes that can set off the light. One type of check engine light is triggered when the oxygen sensor detects an increase in the percentage of Carbon Monoxide produced by a misfiring internal combustion engine. This means that the internal combustion process isn’t burning gasoline or diesel efficiently, and therefore certain emissions are being released into the air.

Issues with your ABS are most likely safety-related, and issues with the powertrain are most likely not. The check engine light comes on if there’s a significant enough problem to affect your driving at this point, where the ABS light certainly wouldn’t.

The check engine light’s meaning has remained the same for about 20 years, with most manufacturers keeping to the same standards with their own proprietary engines. However, there have been changes to what is being monitored with these systems over the last couple of years. Things like tire pressure, fluid level sensors are now being monitored with the OBD II system in newer cars.

Car Engine Light

Some reasons why your check engine light turns on:

My check engine light turned on recently when I was driving to my girlfriend’s house. As you can imagine, this worried me a bit — especially when I got into her driveway, and it stayed on! I took a deep breath and told myself there was nothing to worry about, only to be struck by a new wave of panic with each flashing light. This led me to do a bit of research to squash my fear and educate myself.

I came up with a few reasons why your check engine light might turn on.

  1. Loose fuel cap

This may not seem like a huge issue, but it can lead to more serious concerns if left unattended. Ignoring a loose fuel cap could cause a leak and a poorly running car. If the light comes on, just pull over, reattach the fuel cap, and make sure the light has turned off.

The engine check light is an annoyance that should be addressed as soon as possible. It can take various shapes and forms; however, generally, a flashing orange light informs the driver of an issue with the vehicle.

The engine check light should not be confused with the ABS/ESP lights or the airbag warning light, which will also appear in a different colour and come on solid rather than flashing. The engine management light is often found alongside other lights such as check engine, oil pressure and emissions control.

  1. Transmission

Nearly every vehicle built after 1996 has a computer that controls the transmission. After all, it affects how well you can accelerate and decelerate as well as your fuel economy. If the computer detects a problem with the transmission, it will turn on the check engine light and trigger an engine malfunction.

To understand how the transmission affects tailpipe emissions, you must first understand how they affect the engine performance. The engine control module constantly monitors the efficiency of the transmission input shaft rotation speed. If it detects a problem with this reading, it will set code P0740.

Once the light flashes, it indicates a more serious problem that will require further diagnosis.

  1. Clogged fuel pump

You keep your fuel supply topped up to the brim, you’re vigilant about not letting it go below a certain level, and you monitor the temperature gauge to make sure it doesn’t run too hot or too cool. Your car is looked after like it’s your baby, but there is one thing that will eventually break down… your fuel pump.

The fuel supply system in modern cars consists of a high-pressure pump that pushes fuel to the car’s engine. A control unit located in close proximity monitors the pressure inside the oil feed pipes to the distributor’s head. As rotation speed increases, the intake manifold generates an intake vacuum that is compensated by delivering additional petrol via a fuel pump in front of the engine’s main filter. The fuel filter is located in the feed pipe to the carburetor, where it removes particulates before entering the carburetor to be mixed with air.

The fuel pump sits on top of the fuel filter. So if the fuel filter is clogged, it can also affect the fuel pump. If your engine management light has come on, make sure your fuel pressure is checked.

  1. Damaged catalytic converter

The catalytic converter is a part of your car’s exhaust system that cleans up exhaust fumes from the continual use of gasoline and diesel fuel. In other words, it cleans up pollutants before they get dumped out of the tailpipe and into the environment.

If your converter malfunctions, it causes a much more serious problem than just higher emissions; if that’s not taken care of right away, it can damage the catalytic converter even further and lead to expensive repairs down the road.

  1. Faulty ignition system

The ignition control module (ICM) is a device that monitors the signals from ignition sensors and sends output signals to the ignition coils, which initiate ignition activity. The purpose of the ICM is to maintain a healthy battery charge and keep the spark plugs firing correctly. When it fails, your vehicle won’t start because a misfire limits its ability to turn over.

A faulty ignition system can be easily diagnosed by looking at the code stated in the check engine light. The code can be decoded using a scan tool.

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