Engine Emission Malfunction (Signs, Causes + More)

Engine emission Malfunction

All the warnings that your vehicle might throw out are pretty confusing and slightly worrying, but few more so than the little Check Engine light.

In this article, we’re going to help you understand when you might be experiencing an engine emission malfunction, what can cause the emissions light to come on, and what you may need to do about it.

The engine emission control system in your vehicle is designed to keep harmful emissions as low as possible. When it malfunctions, it is usually a problem with the sensors but it can mean that you have a failed component, a dirty filter, or a worn catalytic converter.

Here are a few steps you need to take to fix engine emission malfunction, which includes:

Step 1: Check the fuel cap.

Step 2: Listen to the engine.

Step 3: Investigate your exhaust fumes.

Step 4: Check your fuel consumption.

Step 5: Reset the warning light.

Step 6: Call a professional.

What Is Your Engine Emission Control System?

What can cause the emissions light to come on? To get to the bottom of what might be causing problems within your emission control system, we first need to get a good understanding of what it actually is, and the different parts involved in making it work.

The emission control system in your car is responsible for limiting the harmful gases that are produced by your engine.

There are a few different kinds of emission control systems and different within them, depending on the type of engine that you have, all designed to combat the gases that come from three main sources:

  • The Exhaust. The exhaust pipe is where the gases are discharged, including hydrocarbons, carbon monoxide, nitrogen and sulfur oxides, trace acids, alcohols, and phenols.
  • The Crankcase. Some hydrocarbons and carbon monoxide also come from the crankcase that houses the crankshaft.
  • The Fuel Tank and/or Carburetor. Hydrocarbons evaporate from the fuel tank (and the carburetor in older cars).

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How To Fix Engine Emission Malfunction

With all that in mind, what can you actually do when you notice that there may be a malfunction with your emission control system?

Don’t worry, we’ve got a simple step-by-step guide that will tell you how to diagnose what is going on, how you can try to solve the problem yourself, and when it’s time to call a professional.

Step 1: Check the fuel cap.

The first thing to do when your vehicle is showing you the Check Engine Light is to make sure that your fuel cap is securely closed and isn’t loose – particularly if you have just filled it up. Sometimes, this is all that has to happen to make that light go away.

Step 2: Listen to the engine.

If it’s not the fuel cap that’s causing problems, then it’s time to investigate the other symptoms to find out where the issue lies.

First, listen out for any misfires that might tell you that it is one of your spark plugs or ignition coils, and not your emissions system, that has failed.

If you are noticing other strange noises, then it may be a catalytic converter problem. This can cost anywhere from $1,000 to $3,000 to replace.

Spark plugs, on the other hand, can be replaced relatively cheaply as they tend to cost less than $100 for a full set.

Step 3: Investigate your exhaust fumes.

If the fumes coming out of your car are particularly dark, then it may well mean that the catalytic converter is not working properly.

If you are noticing a strong smell of gasoline, this usually indicates a pretty serious emissions problem and you should contact a mechanic as soon as possible.

Step 4: Check your fuel consumption.

If you are noticing that you are using up a lot more fuel than usual, then it is likely that one of the sensors within the vehicle is not working properly, or that you have a problem with your EGR valve.

Step 5: Reset the warning light.

If there doesn’t seem to be any other indication that there is a problem with the emission control system, then you can give the warning light a chance to reset to make sure that it is not being shown in error.

To do this, you simply turn off the vehicle, disconnect the battery, leave it for 10 to 20 minutes, then reconnect the battery and start it up again.

Step 6: Call a professional.

For any kind of engine emission malfunction, it may be easiest to simply get in touch with a professional who can sort it out for you.

Diagnosing the problem yourself can be very difficult, and fixing it, more often than not, will mean replacing or repairing a complex component.

What Are The Different Parts Of Your Emission Control System?

In order to limit and reduce how many harmful emissions are released from these places, there are a number of different elements that make up the engine emission control in your vehicle.

Not every system has all of the exact same features, but there are a few that are pretty standard across modern cars today.

Evaporative Emission Control

This helps to reduce emissions and stops you from losing fuel as well. It uses a carbon canister to absorb fuel vapors and releases them back into the combustion chamber.

Your car will also usually have a Positive Crankcase Ventilation Valve (PCV) to inject the fuel vapor into the intake manifold of the engine.

Secondary Air-Injection System

In this system, fresh air is injected into the exhaust stream, either with a pump or an aspirator. This combines the air with unburned hydrocarbons and carbon monoxide to allow for fuller secondary combustion.

Exhaust Gas Recirculation System (EGR)

This system uses a valve to return a small amount of the gas from the exhaust into the combustion chamber via the intake manifold, lowering the combustion temperature and reducing Nitrogen Oxide emissions.

Catalytic Converter

This system houses a metal catalyst, like platinum or palladium, that the gases are passed over. The catalysts induce the hydrocarbons, carbon monoxide, and nitrogen oxide to convert some of them to water vapor, carbon dioxide, and nitrogen.

Diesel Particulate Filter (DPF)

In diesel engines, the DPF is a honeycomb filter that traps soot coming through from your exhaust manifold. The solid particles are collected and then burnt off in a process called regeneration.

How Can You Tell You Have An Engine Emission Malfunction?

Now that we know a little more about what the engine emission control system in your car is, and how many different parts are involved, it’s easier to see how the system might fail and why it can be so complicated to determine what has actually gone wrong.

Unlike a feature like your brake pads – which the car can monitor and simply inform you when they have worn down – the engine emission control has a lot of elements that could malfunction or stop working, so you won’t always get a clear warning about what’s happened.

There are some clues to look out for that may indicate you are experiencing an engine emission malfunction:

  • Check Engine Light. This is the only signal that your car is likely to give you, but very few vehicles will directly indicate that it is an engine emission problem that has caused the light to turn on. Some modern vehicles, however, do have a “Check Emissions” warning.
  • Gasoline Smell. Being able to smell gasoline either in or out of your car is a bad sign. It can mean a leak, and it can be an indicator that your emissions system has a serious malfunction that needs to be addressed as soon as possible.
  • Higher Fuel Consumption. Part of the function of the system is that it reduces how much fuel vapor you lose so, when this fails, some of the gas from your tank will evaporate over time. If your engine control system is not functioning properly, then this can lead to worse fuel economy and you may notice that you’re burning through a lot more gas.
  • Worse Performance. There are a lot of different things that can affect the performance of your car, and a problem with your emissions control system is definitely one of them.

Why Has Your Engine Warning Light Come On?

There are a lot of different reasons why your Check Engine Light may have come on, and not all of them are directly part of the emission control system.

It may be that there is something else going on that you need to address instead, so it’s worth knowing the various reasons why this warning can appear.

The most common issues that trigger the Check Engine Light are:

  • Catalytic converter issues. This is possibly the most common problem with the emissions system, as your catalytic converter can become clogged or worn. If it has failed, you might notice unusual noises or darker smoke coming out of the exhaust pipe.
  • EGR valve problem. This valve can also clog or it can even fail entirely, which will mean your car won’t be running as efficiently and will be producing more emissions.
  • Clogged filter. The diesel particulate filter is another part of an emissions control system that is likely to become clogged over time. Some vehicles have a specific warning message for this filter, but others just use the generic Check Engine Light instead.
  • Oxygen sensor failure. Your oxygen sensor is designed to measure how much unburnt oxygen is in the exhaust system, and if it is not working properly then your ECU will not be able to accurately determine the right air-fuel ratio in the cylinders.
  • Mass Airflow (MAF) sensor failure. This sensor measures how much air is going into the engine and, when it isn’t working properly, you might notice the vehicle rough idling, having problems starting, higher fuel consumption, and frequent stalling.
  • Loose fuel cap. This might seem like a small thing, but your fuel cap is vital for preventing vapor from escaping and maintaining pressure throughout the whole system.
  • Ignition system fault. The spark plugs or ignition coils within your ignition system are vital for causing combustion within the cylinders, and any one of them can wear or fail over time. You might notice misfiring and acceleration issues if they are worn.

Why Is My Check Engine Light On? Easy Fix! >> Check out the video below:


So, what is an engine emission malfunction and how do you solve it? Well, the most common problems that might be occurring in your emission control system are faulty sensors, clogged filters, or a failure with one of the valves or the catalytic converter.

To fix it, first, make sure that the warning light is not telling you that your fuel cap is loose, then consider the other symptoms to get to the root cause. Ultimately, you will probably need to visit a professional for a proper repair or replacement of one of the parts.




Steve P.

Steve is an automotive technician, technical writer, and Managing Editor. He has held a lifelong passion for cars, with a particular interest in cars like the Buick Riviera. Steve is based in Boise, Idaho.

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