Diesel EGR System Service and Diagnostic | AG Automotive

Exhaust gas recirculation systems (EGR) were commonly seen in petrol vehicles throughout the 1970s and 1980s to lower emissions and increase fuel efficiency. The EGR system is designed to recirculate a portion of the nitrogen oxide (NOx), or exhaust gasses, back into an engine’s cylinders. By the 1990s, emission technology had seen significant advancements which allowed the majority of petrol cars to ditch the system entirely. It was around that same time where EGR systems were adopted by diesel cars, light-duty trucks, and heavy-duty engines. It wasn’t until 10 years later after the EGR cooling system was introduced, that cooled EGRs became widely adopted by most light-duty and heavy-duty diesel trucks. EGR systems are still used today in light-duty petrol vehicles for the benefit of increased fuel economy, but not so much for regulating NOx.


The EGR system does have some drawbacks at the cost of recycling and limiting NOx emissions. Car manufactures have had to adapt to EGR technology by reducing oil consumption, increasing fuel injection pressure, adding additional chemicals to diesel fuel, and increasing the manifold boost pressure. Without these preventive measures, the EGR system would see an increase in fuel consumption, exhaust other harmful emissions, cause additional engine wear and reduce an engine’s longevity. 


It is important to understand the benefits and drawbacks that an EGR system provides for your vehicle. This article intends to explain how the EGR system works, its working components, and how you can identify the warning signs of an EGR system that needs servicing. If you have any questions about your EGR  system, call AG Automotive and one of our expert technicians can help you schedule an EGR system service and cleaning today!


 What is an EGR system?


The exhaust gas recirculation system (EGR) is designed to recirculate a portion of the nitrogen oxide (NOx), or exhaust gasses, back into an engine’s cylinders to reduce emissions and provide a small boost in performance. The EGR system consists of 4 main parts; the air intake, valve, cooler, and exhaust point. The recirculation process begins with the air induction system supplying clean oxygen to the EGR system via the air intake. From there, the oxygen will start to combust in the cylinders and, if it wasn’t for the EGR system, would otherwise then be redirected out the exhaust system along with a heap of NOx. Engines are not 100% efficient in combusting diesel fuel, thus creating an excess amount of harmful emissions. Strict emission standards have caused manufacturers to think about alternative solutions to reduce vehicle emissions, and an EGR system is a well-balanced, efficient, and cost-effective solution to this problem. The uncombusted exhaust flows through the cooling system to cool the gasses down before being passed through the valve which regulates the ratio of oxygen and exhaust to be let back into the combustion chamber. On some vehicles, the exhaust gasses are only recirculated after they have flowed through the DPF system. Although diverting the flow through the DPF creates higher pressures that need additional reinforcement, the recirculated exhaust that passes back into the inlet manifold is much cleaner and almost free of all soot. 


 EGR Valves:

This single valve is an integral part of a diesel engine’s EGR system. Its purpose is to regulate the ratio of exhaust gas and oxygen in the intake system. An open EGR valve allows more oxygen to enter the system to dilute the recirculated NOx. This results in the oxygen and NOx burning slower and more efficiently. The additional oxygen lowers the combustion temperature and reduces the amount of NOx being exhausted back into the atmosphere. During startup, the EGR valve gradually opens to allow for some oxygen to help reduce diesel knock at idle. While a vehicle is carrying a heavy load or accelerating, the valve is closed to ensure maximum oxygen is being delivered to the EGR system. 


There are five main types of EGR valves:

  • Digital valve: Almost every vehicle on the road today has an electronically controlled EGR valve. It consists of a solenoid or stepper motor which is regulated by feedback sent to the ECU. The feedback from the valve aids the ECU in regulating exhaust gas flow. 

  • Diesel high-pressure valve: This valve diverts the fast, soot-filled flow of exhaust gas before it enters the diesel particulate filter (DPF). It is a safety net to help avoid the build-up of engine sludge over time. The gas then enters the inlet manifold in the cylinder head. A secondary valve is needed to form a vacuum around the inlet manifold. 

  • Diesel low-pressure valve: Like the high-pressure valve, it diverts the exhaust gasses after they have flowed through the DPF system. The exhaust gasses are only recirculated after they have flowed through the DPF system. Even though diverting the flow through the DPF creates higher pressures that need additional reinforcement, the recirculated exhaust that passes back into the inlet manifold is much cleaner and almost free of all soot.

  • Gasoline valve: Similar to its high & low-pressure counterparts, this valve diverts the exhaust gasses. Cylinder depression creates a vacuum around the intake manifold and draws in the exhaust gasses. The ECU regulates the flow and gas ratio within the cylinder.  

  • Vacuum operated: Commonly used by earlier diesel vehicles, this valve uses a vacuum solenoid to open and close the valve by varying the vacuum pressure to the diaphragm. More modern vacuum-operated valves have a sensor that sends feedback to ECU to ensure the system is functioning properly. 


EGR Cooler:

The function of an EGR cooler is to lower the temperature of the recirculated exhaust gas, reducing the combustion temperature and lowering the amount of NOx being exhausted back into the atmosphere. Without the cooler, the ~1,200°F recirculated exhaust gasses would increase the combustion temperature, ultimately counteracting the function of the entire EGR system and rendering the system useless. Industrial vehicles require a large amount of air intake, produce more NOx, and have faster exhaust flow rates, meaning they require a system that has high-cooling capabilities- this is supplied by the addition of a heat exchanger. For larger, high-demand industrial vehicles, such as a 16V – 4.8L engine, the EGR cooling system needs up to eight high-performance radiators to produce the required mechanical strength needed to ensure peak EGR cooling efficiency. 


How do I know if my EGR system needs servicing?

  • Check engine light is on
  • Increased emissions 
  • Poor engine performance 
  • White smoke from exhaust 
  • Reduced fuel efficiency
  • The engine is knocking while idling or accelerating


The image above is an example of how carbon can build up in the air intake system. This is a common occurrence with EGR systems and ignoring the warning signs can lead to multiple problems like the ones described above. We all know that having your vehicle problems assessed, diagnosed, and by expert mechanics is a given. But it’s even more so to have your EGR professionally cleaned because they have the proper tools, knowledge, and chemicals needed to bring your EGR system back up to factory standards. 


Schedule your EGR system service and cleaning today!

If you are experiencing engine knock while idling or accelerating, poor fuel economy, or increased emissions, Ag Automotive will have you back on the road in no time after we identify that your EGR system needs cleaning. Our expert technicians have the tools and knowledge to test, clean, and replace EGR systems quickly and efficiently. We test each component independently and pinpoint the problem and notify you of the problem and how we can help solve it. We want our customers to know what is happening during every step of the process. Avoiding replacing parts that were otherwise functioning properly. This saves our customers time, money, and vehicle downtime. Our expert mechanics at AG Automotive can easily identify the faulty glow plug and replace it with a properly working one. 


We offer our customers a full-service inspection, service, and/or replacement of their engine’s EGR system. We want the job to be done correctly the first time so we double-check that the EGR system is working properly and meets the manufacturer’s specifications before and after replacement.


A typical EGR cleaning service consists of manual cleaning of an EGR cooler. We remove the cooler and manually clean it by hand and run it through our supersonic washer. While the EGR system is in the vehicle, we do an induction system cleaning if there is a large build-up of carbon deposit in the air intake. If this is the case, it has to be cleaned out by hand using chemical cleaning agents to ensure the air intake is free of soot and transports oxygen properly to the EGR valve.

Don’t Second-Guess the Condition of Your Vehicle

Many auto owners struggle to know if the right work was done the right way on their car. As a courtesy, we provide digital vehicle inspections and photos so you can quickly and easily see what our experienced, professional technicians are seeing. Overall, we go the extra mile to help you make informed decisions on the repair and maintenance plan of your vehicle, so you can drive with confidence every time you get behind the wheel.