EGR Part 1:  What is Exhaust Gas Recirculation and How Does it Work?

Auto manufacturers work hard to improve fuel efficiency and reduce emissions from engine operation and have engineered some pretty impressive ways of doing so. From turbocharging small engines to complex DEF injection systems on diesels, vehicles are emitting far less and going much further on less fuel than they ever have before. One of these technologies, EGR, also works to reduce engine emissions. Unless you have had issues with your EGR valve, you may not have heard of it. In this article, we are going to go over what EGR is and how it works.

What is EGR?

EGR, which stands for Exhaust Gas Recirculation, is a system that diverts a controlled amount of vehicle emissions back into the intake. By introducing exhaust gases to the intake, the engine can operate while emitting fewer NOx gases.

EGR Lowers Combustion Temperatures

Exhaust Gas Recirculation is an effective emissions control tool because it effectively lowers the temperature of combustion. Nitrogen makes up nearly 80% of the air we breathe and is normally benign. But when it’s exposed to extreme temperatures, such as engine combustion, it reacts, producing harmful NOx gasses which are then released as exhaust emissions.

EGR Results in Reduced Emissions

Combustion is the result of igniting a mixture of air and fuel. Oxygen drives combustion. The more oxygen present in the combustion chamber, the hotter the burn, and more NOx gases will be released. By introducing exhaust gases into the intake, the chemical makeup of the air entering the cylinder is changed and has less oxygen. With less oxygen, the combustion temperature is lower, and fewer NOx gasses are emitted.

How Does the EGR System Work?

An EGR valve controls exhaust gas recirculation. The valve meters the flow of exhaust gasses from the exhaust manifold to the intake. The valve positions are open and closed. The degree of opening will vary depending on the conditions of operation. For example, at idle, the engine does not need to make a lot of power, so the valve will open up almost entirely. When you step on the gas, the valve will close to allow more oxygen into the cylinders, creating more power.

EGR on Diesel Engines

Diesel Vehicles have complex emissions control systems. There are two types of EGR systems that diesel engines can utilize, a High-Pressure and a Low-Pressure system. You will find EGR systems on diesel trucks like Duramax, Cummins, and Powerstroke, as well as passenger vehicles like Volkswagen and Audi

High-Pressure Diesel EGR

This system is “high pressure” because the recirculation occurs after intake air is compressed by the turbocharger, and before the exhaust gas enters the turbine. Due to the components’ close positioning to the engine, high-pressure EGR systems can adjust the EGR rate rapidly.

Additionally, because the recirculated exhaust gas is entering the intake tract after the compressor, the turbo is not exposed to soot and carbon deposits, preserving its function for longer.

High-pressure EGR systems are the most common diesel EGR design.

High Pressure EGR system graphic

Low-Pressure Diesel EGR

Low-pressure EGR is a newer technology that places the components on the low-pressure side of the engine (before the compressor and after the turbine). There are two main advantages to low-pressure EGR:

1.) The recirculated exhaust gasses have passed through the DPF (diesel particulate filter). The DPF reduces soot and particulate matter to passing through (and building up in) the EGR system and engine.

2.) The lower pressure of the recirculated exhaust gas means it’s re-entering the engine at a lower temperature. You’ll remember that lower combustion temperatures lead to decreased NOx emissions. Low-pressure EGR systems are far less common than their high-pressure counterpart, especially on production, street-legal vehicles.

low pressure EGR system graphic

EGR Service at Lake City Auto Care

If you are having issues with your EGR system, the teams at Lake City Auto Care can help. We have locations in Hayden, Coeur d’Alene, and Rathdrum, and serve the surrounding communities!

In a future post, we will go over some of the common causes of EGR issues and failure, and the symptoms you may notice.

 Our team members are ASE Certified and have the skills and experience to diagnose and fix EGR issues. Give us a call or schedule an appointment on our website today!

How Do Glow Plugs Work on Diesel Engines?

If you own a vehicle with a diesel engine, you know there are unique components and maintenance items that gasoline-powered car owners do not face. One of these components is the glow plug. Sometimes mistaken for or compared to a spark plug, the glow plug is entirely different in its function. If you are new to diesel, you are probably unfamiliar with how glow plugs work. In this article, we are going to cover glow plug function, types, and maintenance.

Glow Plugs are NOT Spark Plugs

Before we go further, we need to say it. Gasoline-powered cars use spark plugs to “touch off” combustion by providing the air/fuel mixture with a spark during each power stroke. Diesels utilize extremely high cylinder pressure to create the conditions for combustion. To the untrained eye, a glow plug might look similar to a spark plug, but in terms of function, the most common thing between them is the word “plug”.

How Do Glow Plugs Work?

When a diesel is running, the compression stroke increases the temperature of the air in the combustion chamber. This compression provides the heat needed to induce combustion, driving the piston down and creating power. Diesel engine blocks are large (to support high cylinder pressure), and as a result, are slow to warm up. A cold engine block will sap away heat from the compressed air, and without a spark (like gasoline engines get) the initial combustion on startup is difficult or impossible. This is where glow plugs come into play.


Glow plugs are heating elements that warm the air-fuel mixture in the combustion chamber or pre-chamber (IDI engines). The extra heat provided by the glow plug aids in combustion when the engine and intake air is cold on initial startup. This process is known as pre-heating.

Pre-heating changed as diesel technology improved. Early thermostat glow plug systems (we’ll cover glow plug types later) required the driver to manually activate the plug for 20 seconds or more before starting the engine.

The advent of in-cylinder glow plugs allowed the plugs to be activated when the key was turned to the “on” position. A “wait to start” light on the dash would let the driver know when to turn the engine over.

Modern glow plug systems require far less time to achieve the temperature required for startup, typically around 6-8 seconds. To further improve pre-heating speed, newer vehicles activate glow plugs when the doors are unlocked or opened.

Types of Glow Plug

There are two variates of the glow plug. In-manifold systems utilize a single plug, in the intake manifold to heat the air before it enters the combustion chamber. The pre-heating time for an in-manifold plug is longer due to the amount of air that needs to be warmed for combustion.

The second type of glow plug is located in-cylinder. This arrangement uses one glow plug per combustion chamber (or in the case of an IDI engine, one per pre-chamber). The preheating phase is much faster with in-cylinder glow plugs because the area they need to warm is significantly smaller.  

How often do glow plugs need to be replaced?

Glow plugs typically last around 100,000 miles before needing to be replaced. You will not need to worry about them too often during the time you own your diesel vehicle.

Are my Glow Plugs Bad?

There are a few indicators of faulty glow plugs, most of which will be pretty obvious.

Hard Starting or No Starting

The core function of glow plugs is to aid in starting the engine. If your plugs are faulty, it may be difficult or impossible to start your diesel vehicle on a cold morning.

Misfires on Startup

Faulty glow plugs will impact combustion and can cause misfires. These will not last long as the engine gets warm.

White or Black Smoke on Startup

Unburnt fuel can exit the tailpipe in the form of white or black smoke. This can be a sign of bad glow plugs. Once the engine is running, the fuel will be burning like normal, and the smoke will stop.

Issues NOT caused by faulty glow plugs

Some issues are often attributed to defective glow plugs but aren’t caused by them. The most common issues we see attributed to failed glowplugs are reduced fuel economy and reduced power or acceleration.

These issues really can’t be attributed to glow plugs. The plugs are active for a few seconds before and after startup, so they are not even on when the vehicle is moving. If a glow plug is causing a startup misfire, then for those first few seconds of operation fuel economy might be lower, but again, once you are driving, any reduction in fuel economy would stem from a different problem

Issues with Glow Plugs? Lake City Auto Care Can Help

We are diesel experts at Lake City Auto Care. The teams at our three locations in Hayden, Rathdrum, and CDA, ID are equipped to work on your diesel, whether it’s an F-350 Powerstroke or a Jetta TDI. Give us a call or schedule an appointment at one of our locations today!