EGR (Exhaust Gas Recirculation) System

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EGR (Exhaust Gas Recirculation) is one of the On-Board Diagnostics (OBD-II) systems related to emission. The EGR system is a pivotal element in reducing harmful emissions, making the engine run better, and improving fuel efficiency. Let’s learn further about the EGR system and how it actually works in more depth.

Purpose of EGR System

The main goal of the EGR system is to cut down on the amount of Nitrogen oxides(NOx) that comes out of the engine. NOx is a dangerous pollutant that makes smog and makes it hard to breathe. By sending some of the exhaust gas back into the engine, the EGR system cuts down on the amount of oxygen that can be burned in the combustion chamber. This lowers the temperature and cuts down on NOx emissions.

The EGR system does more than just cut down on emissions. It also improves fuel efficiency and overall engine performance. By reusing the exhaust gas, the engine is able to burn fuel more efficiently, which saves money on gas. By reducing the amount of heat made during combustion, the EGR system also helps keep the engine at the right temperature.

Purpose of EGR System

By cutting down on the amount of oxygen that can be burned in the combustion chamber, the EGR system helps keep the combustion temperature low. As the engine burns fuel, it creates heat. A higher temperature can cause dangerous pollutants like nitrogen oxides to form. By cutting down on the amount of oxygen that can be burned, the EGR system reduces the temperature of combustion. This helps cut down on NOx emissions and keeps the engine at the optimum temperature. This not only cuts down on pollutants but also makes the engine run better and more efficiently.

EGR System Components

The EGR system includes the EGR valve, the EGR vacuum solenoid, the EGR position sensor, and the engine control module (ECM). These include:

The EGR valve regulates exhaust gas flow into the engine. EGR vacuum solenoid controls valve vacuum. Mechanical linkages and vacuum lines operate the EGR valve near the engine’s intake manifold. 

The EGR vacuum solenoid opens and closes the valve. The engine-mounted solenoid controls vacuum pressure to the EGR valve. This opens and closes the EGR valve at the right periods to recirculate exhaust gas into the engine.

The EGR position sensor has the function to check the EGR valve’s position. The ECM employs sensor feedback to regulate the EGR valve and ensure proper operation. The EGR position sensor will set an error number and activate the Check Engine light if it detects EGR valve difficulties. 

The ECM monitors and controls the EGR operation. It opens and closes the EGR valve based on the EGR position and oxygen sensor data. To maximize engine performance and reduce emissions, the ECM also regulates fuel injection and ignition timing. The Check Engine light will illuminate if the ECM detects EGR system problems and stores a DTC in memory.

Types of EGR Systems

There are four types of EGR systems: vacuum-operated EGR systems, electronic EGR systems, pneumatic EGR systems, and hydraulic EGR systems. Each controls EGR valve opening and closing differently.

1. Vacuum-Operated EGR System

The vacuum-operated EGR system uses a vacuum to control the EGR valve’s opening and closing. Vacuum-controlled EGR systems are the most frequent. A vacuum signal opens and closes this EGR valve. Vacuum solenoids manage engine intake manifold vacuum signals. The solenoid sends a vacuum to the EGR valve when activated. Exhaust gas enters the intake manifold when the EGR valve opens. Long-used vacuum-based EGR systems are simple and reliable.

2. The Electronic EGR System

The electronic EGR system uses an electronic signal from the ECM to control the EGR valve. The ECM regulates the EGR valve in the electronic EGR system. With this system, the ECM examines engine sensors and determines the best EGR flow rate based on engine performance. The ECM then opens or closes the EGR valve to control EGR flow. The electronic EGR system can better control EGR flow, improving engine performance and reducing emissions.

3. The Pneumatic EGR System

The pneumatic EGR system uses compressed air to control the EGR valve. The compressed air operates the pneumatic EGR valve. This system uses an air pump and a solenoid valve to compress air. The solenoid valve sends compressed air to the EGR valve. EGR valves allow exhaust gas into the intake manifold. Several cars use pneumatic EGR systems, which are less prevalent than vacuum-operated and electronic EGR systems.

4. The Hydraulic EGR System

The hydraulic EGR system is one of the less prevalent types of EGR systems. It regulates the flow of exhaust gas into the engine by using hydraulic pressure. The volume of exhaust gas that is recirculated through the engine is controlled by a valve in this EGR system, just as it is with other EGR systems.

EGR System Operation

The EGR system works by recirculating a portion of the engine’s exhaust gas back into the intake manifold. The EGR valve regulates the amount of exhaust gas that is recirculated. When the engine is running, the ECM monitors various engine parameters, such as engine load and temperature, to determine when to open the EGR valve.

When the EGR valve opens, exhaust gas flows into the intake manifold and mixes with the fresh air/fuel mixture. This reduces the amount of oxygen available for combustion, which lowers the temperature and reduces NOx emissions. Once the EGR valve is closed, the engine returns to normal operation.

EGR Diagnostic Trouble Codes (DTCs)

The EGR system, like any other component in a vehicle, is susceptible to malfunction, which can result in the accumulation of diagnostic fault codes (DTCs). These are some common EGR-related DTCs with the meaning

To figure out what’s wrong with EGR DTCs and fix them, you must do a full examination of the EGR system. Most EGR problems are caused by a broken EGR valve, a clogged EGR passage, or a vacuum leak. 

Importance of Maintaining EGR System

Taking care of the EGR system is important for a number of reasons. With regular maintenance, the system works at its best, reducing harmful emissions and getting the most mileage out of each gallon of gas. If you don’t do maintenance, you might have to pay for expensive repairs, your engine might not work as well, or you might not meet emissions standards, which can lead to fines and other pricey expenses. 

Benefits of Maintaining the EGR System

One of the main reasons to keep the EGR system well-maintained is that it helps to cut down on harmful emissions. As we’ve already talked about, the EGR system is in charge of sending the exhaust gas back into the engine to cut down on NOx emissions. Regular maintenance of the whole components of the EGR system makes sure that the system works right and eventually reduces emissions. 

Keeping the EGR system well-maintained also saves money on gas. By reusing the exhaust gas, the amount of fuel needed to run the engine can be cut down. This helps the car get better gas mileage that’s also more environmentally friendly.  

Consequences of Ignoring EGR System Maintenance

Bad things can happen if you don’t properly maintain the EGR system. Carbon buildup and other leftovers can stop the EGR valve from operating properly over time. This hurts how well the engine works. This can make the car run poorly, use more gas, and even wreck the engine.

Also, your car might fail an emissions test if you don’t properly maintain the EGR system. Neglecting maintenance can lead to repairs that cost a lot of money and fines, as well as more pollution that hurts the environment. When the EGR is broken, you will have to fix it and pay a fine.


The EGR system has become a key part of lowering emissions and saving gas in today’s cars. It’s an important part of the OBD-II system, and it’s made up of the EGR valve, the vacuum solenoid, and the position sensor. All of these parts work together to bring exhaust gas back into the engine. Maintenance is needed to make sure that the system works well and efficiently.

If you don’t do maintenance, it can hurt your engine’s performance and gas mileage, among other things. It’s important to have a qualified mechanic check out and fix any problems you think might be happening. By taking care of your EGR system, you can reduce the damage you do to the environment and get the most out of your car.

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