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EGR valve. Taking NOx Emissions Seriously.

How to install

As an integral part of the vehicle's engine management system, the so-called exhaust gas recirculation (EGR) valve serves to return a precisely calculated amount of exhaust gases to the engine intake system to improve its efficiency, reduce fuel consumption and reduce nitrogen oxides in exhaust gases. As emission reduction requirements increase, the EGR valve will play an increasingly important role, so you should know what it is for, why it fails, and how to replace it if it breaks.

The air we breathe is almost 80 percent nitrogen. However, when exposed to extremely high temperatures in the combustion chamber, up to 1370 °C, this normally inert gas becomes reactive and forms harmful nitrogen oxides, or NOx, which are then released through the exhaust system into the atmosphere. To keep these emissions to a minimum, the EGR valve delivers a precisely calculated amount of exhaust gases to the intake system, thereby changing the chemical composition of the air entering the engine. With less oxygen, the diluted mixture burns more slowly, reducing combustion chamber temperatures by up to 150°C and reducing NOx formation, resulting in a cleaner, more efficient exhaust.

The EGR valve has two main positions: open and closed, although it can assume any intermediate state. When starting the engine, the EGR valve is closed. During idling and at low speeds, a small amount of power and therefore a small amount of oxygen is enough, so the valve gradually opens. At idle, it can be 90% open. However, when more torque and more power is needed, such as under full acceleration, the EGR valve closes to allow more oxygen to enter the cylinder.

In addition to reducing NOx emissions, EGR valves can be used in small displacement GDi engines to reduce pumping losses as well as improve fuel efficiency and reduce knocking. In diesel engines, it also helps reduce idling knock.

Although there are several types of EGR valves—earlier systems use vacuum valves, while more modern vehicles use electronically controlled valves—the main types can be distinguished as follows:

High pressure diesel EGR valves divert a fast soot-rich exhaust gas stream before it enters the particulate filter - the soot can combine with oil vapor and form sludge. The gas then flows back into the intake manifold, either through a pipe or through internal openings in the cylinder head. The auxiliary valve is also used to create a vacuum in the intake manifold, as it does not naturally occur when a diesel engine is running.

Low pressure diesel EGR valves divert exhaust gas after it has passed through the particulate filter. This gas moves at a slower speed, but it is almost completely free of soot. The gas then flows back into the intake manifold through the pipe.

Gasoline EGR valves divert exhaust gases in the same way as their high pressure diesel counterparts. When a vacuum is created in the cylinder, the exhaust gases are drawn into the combustion chamber, and the volume of their supply is regulated by the opening and closing of the EGR valve itself.

Vacuum operated EGR valves have an electrovacuum valve to vary the amount of vacuum applied to the diaphragm and in turn open and close the EGR valve. Some valves also have feedback sensors to signal their position to the ECU.

Digital EGR valves are equipped with a solenoid or stepper motor and in most cases a feedback sensor. These valves receive a pulse-width modulated signal from the ECU to control the flow of exhaust gases.

What are the causes of broken EGR valves?

Exhaust gas recirculation valves operate in harsh environments and can wear out over time. However, the single main reason for their failure is carbon deposits along the exhaust gas recirculation channels and the intake system. Over time, this clogs the tubes, exhaust passages, and eventually the valve plunger mechanism, causing it to either get stuck open or closed. Malfunctions can also be caused by a ruptured or leaking valve diaphragm.

What are the symptoms of a bad EGR valve?

EGR valve symptoms are similar to other engine management system problems. For this reason, EGR malfunctions remain a headache for many auto mechanics. However, there are a few signs to look out for:

• The check engine light is on. As with most engine management system components, a problem with the EGR valve can cause the check engine light to come on.
• Engine malfunction. If the valve is stuck open, the air/fuel mixture will be compromised, resulting in engine problems such as reduced power, sluggish acceleration, and rough idle. It can also lead to pressure leaks in the turbocharging system, causing the turbocharger to work harder.
• Increasing NOx emissions. When the EGR valve remains closed, high temperatures occur in the combustion chamber, leaving a large amount of unburned fuel in the exhaust, resulting in increased NOx emissions and reduced fuel efficiency.
• Engine detonation. Elevated temperatures and high NOx emissions can also lead to increased knocking, which can be recognized by engine knocking.

Given the variety of EGR valve types, it is always best to follow the troubleshooting procedures detailed in the service manual, however there are a few standard steps that can help pinpoint the problem:

• Read EGR valve trouble codes with a scan tool.
• Check that all vacuum lines and electrical connections are connected and located correctly.
• Using a vacuum gauge, check the degree of vacuum in the vacuum hose at 2000-2500 rpm. No vacuum at normal operating temperature may indicate a loose hose, a clogged or faulty vacuum switch with fittings or an EV valve, or a faulty vacuum booster/pump.
• Check the electrovacuum valve while the engine is running. On EC EGR valves, activate the solenoid with a scan tool and check the vacuum at the end of the pipe. If the valve does not open when energized, is stuck open or closed, or has rust on the electrical connection, a loose wire connection, or a bad ground, the EGR system will not function properly. Before replacing a valve, determine the root cause of its malfunction.
• If possible, check valve stem movement at 1500-2000 rpm. If the valve is functioning correctly, the valve stem should move. If it does not move when there is a vacuum, then the valve is defective.
• Vacuum directly on the EGR valve using a hand held vacuum pump or scanner, depending on valve type. If no changes are detected at idle, then either the EGR valve is faulty, or the EGR channels are completely blocked. If the engine idles intermittently or stalls, the problem is caused by a faulty control system.
• Remove the EGR valve and check it for carbon deposits. If possible, remove carbon deposits, being careful not to foul the membrane.
• Check that the exhaust gas recirculation duct in the manifold is not blocked. Clean it if necessary.

Common Fault Codes

Late model EGR valves are characterized by the following fault codes:

• P0400 - Malfunction in the exhaust gas recirculation system.
• P0401 - Insufficient Exhaust Gas Recirculation Flow.
• P0402 Excess EGR flow.
• P0403 - a malfunction of the electrical wiring of the exhaust gas recirculation system.
• P0404 - Incorrect value in the EGR valve circuit.
• P0405 - low signal level in circuit "A" of the sensor of the exhaust gas recirculation system.
• P0406 - high signal level in circuit "A" of the sensor of the exhaust gas recirculation system.
• P0407 - low signal level in the circuit "B" of the sensor of the exhaust gas recirculation system.
• P0408 - high signal level in the circuit "B" of the sensor of the exhaust gas recirculation system.
• P1403 - low voltage in the control circuit of the exhaust gas recirculation valve.
• P1404 - exhaust gas recirculation system - valve stem stopped in the closed position.
• P1405 - high voltage in the control circuit of the exhaust gas recirculation valve.
• P1406 - positioning error of the valve stem of the exhaust gas recirculation system.

• Remove the engine cover first.
• Then loosen the electrical cable connected to the valve, disconnect the wires and/or vacuum lines and check for signs of damage.
• Remove the mounting screws and inspect the valve for damage, corrosion, or deposits.
• Thoroughly clean the EGR valve mounting surface and install a new valve and gasket. You should also remove carbon deposits from the EGR intake valve.
• Align the EGR valve with the bolt holes and gasket and reattach to the body.
• Tighten all fasteners to the recommended torque.
• Then reconnect the vacuum lines and/or electrical connections.
• When finished, use the diagnostic scanner to reset the signal that turns on the check engine light and check for other errors. Make sure the fault indicator is off. Then do a road test. In many vehicles, adaptation now requires an EGR valve reset. This allows the ECU to remember the stop position when the valve is open and closed. Otherwise, the valve may break and fall into the manifold.

Repair is a delicate matter, or How we reanimated the engine

Most often, such "illnesses" as wear of the main bearings and rings, valve burnout interfere with the normal functioning of the power unit.

In order to see where, and most importantly, how a car engine is repaired, we arrived at the transport and logistics center "Belmagistralavtotrans", located not far from Minsk. It is here that the largest service center for the repair and maintenance of Volvo trucks is located, whose specialists were trained in Volvo training centers. The company's own fleet includes 150 cars, but, according to experts, it is extremely rare to have to repair your cars. 85% of repairs are customer car repairs.

The very first piece of advice given to us by Vyacheslav Godlin, chief engineer of Belmagistralavtotrans, is to pay attention to the service station class: "Class A" service center can perform warranty service as well. is that today there is a huge number of electronic components, which can be programmed only by directly contacting the factory and requesting factory parameters. Certified service centers have this opportunity" , he explained.

In general, of course, auto repair can be compared with a surgical operation. What can I say, let's see.

Do you feel it? The room is imbued with the spirit of anxious waiting

Drivers usually wait in a room similar to this for the diagnostician's verdict. The client talks about the problems, after which the computer diagnostics actually take place. We propose to go a little further and see what is happening in the "operating room".

"Sick" line up

Today there are not so many "sick" people. One car is undergoing scheduled maintenance, the tires of the second are being deepened, the third is waiting for the gearbox to be repaired. And that's what we have to figure out with the fourth!