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In the previous section we discussed the basic problems of engine thermal stress. Now let us focus on the issues related to the EGR system as well as the effect of high temperature on engine oil fatigue
3. Exhaust gas recirculation (EGR) and thermal breakdown

Most people who repair cars know that exhaust gas recirculation (EGR) is a method to reduce contaminant emissions from combustion engines. A question that often gets asked is what kind of contamination is reduced by this system? This should now be clarified: the EGR system reduces the amount of nitrogen oxides (NOX) in exhaust gases emitted during engine operation.  

In the ideal process of combustion in an engine, the fuel (made of hydrocarbons, i.e. carbon and hydrogen compounds) is burnt (reacts with oxygen from the air), which results in the creation of carbon dioxide and water as well as energy, of course.  

 So car engines are “fed” with atmospheric air and fuel.  

The air that surrounds us contains over 20% of diatomic oxygen (O2) and 78% of diatomic molecular nitrogen (N2) with the remaining components occurring in significantly smaller proportions. Under normal conditions, approx. 99% of atmospheric gas volume is nitrogen and oxygen, elements that are “reluctant” to combine to form nitrogen oxides (NOX). The formation of such oxides is quicker at high pressures and temperatures – unfortunately, such conditions occur in the car engine combustion chamber. 

Reintroduction of a controlled amount of exhaust gases to the intake manifold causes a decrease in the temperature of the engine combustion chamber. This happens because nitrogen oxides (NOX) are formed at high temperature and pressure, while the recirculation of a carefully controlled amount of exhaust gases (controlled by the EGR valve opening) mainly affects the reduction of emitted NOX by reducing the temperature in the engine combustion chamber.  


Therefore improper operation of the EGR system directly results in a higher temperature in the combustion chamber, which can lead to additional thermal damage to both the engine and the oil. 

4. EGR system faults

Hundreds of EGR valves are replaced every day after fault code diagnoses, but replacement often only eliminates the problem for a short while. Consequently, every day the technical departments of spare part manufacturers and distributors receive a large number of warranty complaints regarding EGRs they have manufactured and sold. 

 The faults found are usually divided into two broad categories: general problems (e.g. clogging with oil-derived/carbon sediment) and problems specific to a particular vehicle. Let us start discussing these specific problems. 


A) EGR valve with pneumatic control/EGR valve with pneumatic control and position sensor. 

Figure 7a. Pneumatic EGR valve
Figure 7a. Pneumatic EGR valve 
Figure 7b. Electropneumatic pressure converter (EPW) valves
Figure 7b. Electropneumatic pressure converter (EPW) valves 

These valves are activated by the vacuum source modulated by an electropneumatic pressure converter (EPW). The vacuum at this actuator (EPW) is regulated using a pulse-width modulated (PMW/RCO) signal generated by the injection computer, depending on the system status (mainly temperature, speed, load). 

Such an EGR valve should be replaced only after performing a series of related procedures: checking and cleaning the pneumatic tubes and channels for the intake manifold, checking the injection system operation, the mechanical state of the engine (see if soot has accumulated on the EGR valve) and crankcase ventilation system (see if there is oil on the valve), checking the vacuum source, checking the electropneumatic actuator (measure the inlet and outlet pressure, measure and review the PWM control signal), checking the boost control system operation (variable geometry actuator/wastegate), checking the diesel particulate filter filling level and checking the operation of the flowmeter/inlet valves/turbo valves. 


B) Electrically regulated EGR valve 

Figure 8a. Electrically regulated EGR valve
Figure 8a. Electrically regulated EGR valve 
Fig. 8b EGR valve with electric control and exhaust gas cooler
Fig. 8b EGR valve with electric control and exhaust gas cooler 

These valves are activated directly by the injection computer using a pulse-width modulated (PMW/RCO) signal, which is generated depending on the system status (mainly temperature, speed, load). 

The above-mentioned verification procedure remains current for these components – the EGR valve should be replaced only after several relevant checks have been performed: remember to check and clean the gas circulation tubes in the exhaust header, check the operation of the injection system and all items mentioned previously for systems with pneumatic control.  

Moreover there are circumstances in which specific errors appear – new EGR valves which do not work after replacement – error codes appear immediately after their installation. In these circumstances it is necessary to perform the basic step of regulating/setting with a diagnostic tester. Another fact to be noted is the need to frequently update injection computer software and re-adjust when changes have been made. 

 See some examples below. 
When exchanging the EGR valve in many VW, Seat, Škoda and Audi engines, the P0400 series of errors occur (e.g. P0400 (16784) exhaust gas recirculation – flow malfunction; P0401 (16785) exhaust gas recirculation (EGR) – flow insufficient; P0402 (16786) exhaust gas recirculation – excessive flow detected; P0404 (16787) exhaust gas recirculation (EGR) – open position performance). The workshop should not limit itself to just replacing the valve. In addition to specific cleaning operations, an adaptation process is required – basic system setting. The basic setting (adjustment) should be performed using a diagnostic tester
For Opel vehicles (Agila 1.0i/1.2i; 12V/16V, Astra G/H/Mk IV/Mk V 1.2i/1.4i; 12V/16V, Corsa C 1.0i/1.2i/1.4i; 12V/16V, Meriva 1.4i 16V, Tigra B 1.4i 16V), when replacing the EGR valve, P0400 errors appear, the engine management light comes on (MIL ON) and the signal from the potentiometer monitoring the valve position is outside the tolerance range. 
In this event, the workshop should also not limit itself to just replacing the valve. In addition to thoroughly cleaning and checking the engine assembly components, an injection computer software update is necessary (generally it will accept larger potentiometer signal tolerances resulting from hysteresis). 
The necessary verification and updating of the injection computer operating software also applies to other applications; for example, engines in the Seat Cordoba, Seat Ibiza, Skoda Fabia and VW Polo 1.2 12V. In these engines, thermal damage to the EGR valve often occurs after a relatively short service life (during the warranty period). Diagnostics will reveal the same P0400 errors (DTC) (OBD standard errors P0401, P0402, possibly P1403; car manufacturer-specific errors 01265, 16785, 16786, 17811). In addition to normal replacement procedures, the software version needs to be checked and updated, if needed (for BME engine codes, a version later than 7000–7001; for AZQ engine codes, a version later than 5323–5329). 
The second type of damage occurs much more often – valve blockage caused by massive accumulation of soot and/or burnt oil sediment. Common signs are lack of power, uneven operation when idling, slow start-up and P0400 error codes, and are not associated with material or manufacturing defects. 

Electrically controlled EGR valve with massive soot accumulation and Fig. 9b Electrically controlled EGR valve with massive soot accumulation – Renault.

A frequent problem with electrically controlled EGR valves is blockage from the ingress of foreign matter into the valve area. Here the common signs are lack of power, uneven operation when idling, slow start-up, P0400 error codes (possibly P1444, P1678) and are not associated with material or manufacturing defects. In many Opel petrol engines, catalyst fragments can be found blocking the EGR valve in the open position. 

 There are situations where EGR valves do not work after installation because of mechanical valve damage – as in BMW vehicles (F26, F30, F31, F32, F36, F45, F46, F82, F83) on diesel engines of 1.5/1.6/2.0 litres. This fault does not result from incompliance with standards but from lack of knowledge of the proper installation procedure. 

Figure 10 a, b. EGR valves for BMW 1.5/1.6/2.0 litre diesel engines.
Figure 10 a, b. EGR valves for BMW 1.5/1.6/2.0 litre diesel engines. 

Usually workshops perform jobs related to any electrical components, more particularly on electrical components (connecting/disconnecting EGR electrical contacts) without power supply to the electrical system (ignition off, clamps disconnected from the battery). Only after the installation/removal procedures have been completed can the ignition be turned on, errors cancelled using a diagnostic tester and the basic settings configured. 

Using the above procedure for the previously specified BMW vehicles results in destruction of the EGR valve assembly. Proper installation is performed without electric connected but with use of a diagnostic tester. Before fitting the EGR valve in the engine assembly, the EGR valve electrical connection should be connected; with the ignition turned on, connect the diagnostic tester to the OBD port and select the specific procedure (EGR valve replacement); then the injection computer will send a PWM command signal which will cause the valve stem to move above the rest position. Only then may the new EGR assembly be mechanically installed (the installation screws may be tightened). Installing the EGR valve without using a diagnostic tester causes irreversible damage to this actuating element and is not covered by the technical warranty. 
EGR valves with electric control and exhaust gas cooler (Fig. 8b) typically generate a large number of warranty complaints. Simple replacement of the EGR valve (especially for VW diesel 1.6–2.0 engines) often results in a quick reoccurrence of the faults. Some characteristics of these events: you cannot simply remove the old valve and install a new one. It is necessary to buy and install the replacement parts in accordance with the information provided by EGR valve manufacturers. 

Figure 11a. Photo of the EGR valve and relevant parts required for proper installation and Figure 11b. List of parts required for proper installation (order codes)

Software update is required for injection computers (applications are subject to corrective action, discontinuation, EA 189 campaign). 

 For 1.6 engines, an additional installation is required – a flow straightener (device providing laminar air flow) before the air-mass meter. 

Removal and cleaning of the inlet manifold is required (as well as the purchase and replacement of manifold seals – these must not be reused). It is also necessary to observe all service steps applicable to those engines that are affected by the issue – in particular those related to the flow of gases aspirated and recirculated in the engine; one such piece of technical information specifies that modification of the recirculated gas flow by the change of the marker location between the pipe and the suction header is mandatory. 

Figure 12. Typical sediment presentation found at disassembly at an approx. mileage of 60,000 miles (100,000 km) and Fig. 13. Mechanical repair is needed in the area marked with the blue circle; this should be done before removal and rotation.

What should be remembered here? 

Exhaust gas cleaning systems, in particular EGR, must be maintained to a faultless technical condition; system faults here may lead to thermal failure, oil thermal fatigue and, under extreme conditions, serious engine failure.  

To be certain that the coolant – and more importantly, the engine oil used – has the optimal properties (including additives specific to the engine and exhaust gas cleaning system which they will serve), select the appropriate oil for your car using the Castrol website: 

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This way you can ensure that you have selected the appropriate oil designed specifically to protect your engine, both directly by ensuring optimal lubrication and indirectly by protecting the exhaust gas cleaning system.