Originally, exhaust gas recirculation(EGR) was used to reduce fuel consumption in gasoline engines. Today, EGR is generally used to reducenitrogen oxide emissions in bothgasoline and diesel engines. There are two types of systems:
In a high-pressure exhaust gasrecirculation (EGR) system, a portion ofthe exhaust gases is tapped directlybehind the exhaust valve and fed backinto the intake air in the combustionchamber via the EGR valve, whichreduces the intensity of combustion.EGR valves operate pneumatically, via apressure converter, or are directlycontrolled electrically by a PWM signal.
As part of further pollutant reduction,the EGR valve was combined with anEGR cooler to form an EGR module. Bycooling the exhaust gases before entry,a further reduction of nitrogen oxides isachieved, which is usually deactivatedduring the warm-up phase by anelectrically controlled bypass valve.
Under unfavorable driving conditions,the EGR module is damaged byaggressive exhaust condensate.Additionally, product improvementmeasures by the vehicle manufacturercan sometimes lead to higher thermalstress, which may cause a failure after ashort time. Depending on the vehicle,replacing the EGR module can take upto 10 hours, as adjacent pipes andsensors may also be affected.
Modern EGR modules operate with apotentiometer and are monitored by theengine control unit (ECU) as part of theOn-Board Diagnostics (OBD) system.The mass air flow sensor plays animportant role in enabling controlledEGR. The intake fresh air can becalculated from the engine speed andintake air temperature and comparedwith the stored target values in the ECU.If there is a significant deviation, thecheck engine light illuminates and thevehicle logs a fault in the data memory.
Due to the stricter Euro 6 standard andlimited operating conditions, the low-pressure EGR system has meanwhilebecome standard equipment in everynew vehicle. In this system, the exhaustgas is taken only after the particulatefilter and, for example, recirculatedbefore the turbocharger. This ensuresthat the recirculated exhaust gas iscleaned, which prevents coking of theEGR cooler. However, due to the lowerexhaust gas pressure in this case, anadditional. A throttle valve must be installed behindthe particulate filter. By closing it, theexhaust gas pressure is increasedagain. Monitoring is usually carried outby an additional pressure or differentialpressure sensor.
A combination of both systems ispossible and ensures a high efficiency.
Dangers of Manipulation
To avoid the often considerable laborinvolved in the event of a failure,dubious providers offer updates for theengine control unit that simulate an EGRsystem regardless of its actualcondition. These modifications causealtered exhaust emissions, resulting inthe vehicle’s operating license beingrevoked. Such changes are alwaysmarked with a timestamp, allowing theexact time of the intervention to bedetermined.
Due to the manipulation of the controlunit, the EGR system is subjected toeven higher stresses. Since exhausttemperature sensors are sometimesalso tampered with, this can lead toexcessive heating of the module andconsequently to a fire in the vehicle.
A professional, albeit labor-intensive,replacement is therefore unavoidable.
