Integrated into a vehicle’s engine management system, the aptly named exhaust gas recirculation valve, or EGR valve for short, circulates finely measured amounts of exhaust gases into the engine’s intake system to increase engine efficiency, reduce fuel consumption and reduce NOx emissions.
With increasing pressure to reduce emissions, the EGR valve will play an increasingly important role moving forward. It is important to know what it does, why it fails, and then how to replace it.
Types of EGR valve
Although there are several types of EGR valves – earlier systems use a vacuum valve, while newer vehicles are electronically controlled – the main types can be summarized as follows:
- High-pressure diesel valves deflect large amounts of soot in the exhaust gas with high flow before it enters the diesel particulate filter – soot can combine with oil vapor to form sludge. The gas is then routed back to the intake manifold either through a tube or cylinder head bores. The secondary valve is also used to create a vacuum in the intake manifold, as this naturally does not occur in diesel engines.
- Diesel Low-pressure EGR valves divert the exhaust gas after it has passed through the diesel particulate filter – this gas has a lower flow, but is almost completely free of soot. The gas is then routed through the tube back to the intake tube.
- Gasoline EGR valves divert exhaust gases, similar to the high-pressure diesel equivalent. The vacuum created by the compression of the cylinder draws in the exhaust gases and the flow is regulated by the opening and closing of the EGR valve.
- Vacuum operated EGR valves use a vacuum solenoid to apply vacuum to the diaphragm and in turn open and close the EGR. Some valves also include a feedback sensor that informs the ECU of valve position.
- Digital EGR valves have a solenoid or stepper motor and in most cases a feedback sensor. These valves receive a pulse width modulated signal from the ECU to adjust the exhaust gas flow.
How does an EGR valve work?
To minimize this, the EGR valve allows a precise amount of exhaust gas to enter the system’s intake system, effectively changing the chemical composition of the air entering the engine. With less oxygen, the diluted mixture now burns more slowly, lowering combustion chamber temperatures by almost 150°C and reducing NOx production for a cleaner, more efficient exhaust. Almost 80% of the air we breathe is nitrogen. But when exposed to the extremely high temperatures of the combustion chamber, plus 1,370°C, the normally inert gas becomes reactive, producing harmful nitrogen oxides, or NOx, which are then released into the atmosphere through the exhaust system.
The EGR valve has two main settings: open and closed, although the position can vary in between. When the engine is started, the EGR valve is closed. At idle and low speeds, only a small amount of power and therefore only a small amount of oxygen is required, so the valve opens gradually – at idle it can be up to 90% open. However, when more torque and power is required, such as during full acceleration, the EGR valve closes to ensure that as much oxygen as possible enters the cylinder.
In addition to reducing NOx, EGR valves can be used in downsized GDi engines to reduce pumping losses and improve both combustion efficiency and knock tolerance. For diesel, this can help reduce diesel fuel at idle.
Why do EGR valves failed?
EGR valves operate in a hostile environment, so they wear and tear over time. However, the biggest cause of failure is the accumulation of carbon particles in the exhaust gases in the passages of the EGR and intake system. Over time, this clogs the pipes, exhaust passages, and eventually the valve piston mechanism, causing it to either open or close. Malfunctions can also be caused by a rupture or leakage of the valve diaphragm.
Common EGR fault codes
On late model EGR valves the following fault codes are common:
- P0400: EGR flow malfunction
- P0401: EGR insufficient flow detected
- P0402: EGR excessive flow detected
- P0403: EGR circuit malfunction
- P0404: EGR circuit range/performance
- P0405: EGR sensor A circuit low
- P0406: EGR sensor A circuit high
- P0407: EGR sensor B circuit low
- P0408: EGR sensor B circuit high
- P1403: EGR solenoid low
- P1404: EGR system – closed valve pintle error
- P1405: EGR solenoid high
- P1406: EGR system pintle position error
What to look out for in a failing EGR valve?
The symptoms associated with EGR valve failure are similar to many other engine management components, and because of this, EGR failures continue to be a source of headaches for many technicians. However, there are some signs to look out for:
- Check Engine Light: As with most engine management components, a problem with the EGR valve can trigger a check engine light.
- Engine Performance Problems: When the valve is open, the vehicle’s air-fuel ratio is cut off, causing engine performance problems such as reduced power, poor acceleration, and rough idling. It can also create turbo boost pressure leaks that cause the turbo to work harder.
- Higher NOx emissions: When the EGR valve remains closed, high combustion chamber temperatures leave a lot of unburned fuel in the exhaust gas, increasing NOx emissions and reducing fuel economy.
- Engine Knocking: Higher temperatures and NOx can also cause more detonation or knocking, which is heard as a knocking noise in the engine.
Troubleshooting an EGR valve
When considering the different types of EGR valves, it’s always best to follow the troubleshooting procedures in your service manual, but there are some general steps to take when determining the diagnosis:
- Read fault codes for electronically controlled EGR valves using a diagnostic tool.
- Check that all vacuum lines and electrical connections are properly connected and positioned.
- Use a vacuum gauge to check vacuum line vacuum at 2000-2500 rpm. Vacuum at normal operating temperatures does not indicate a loose hose, a blocked or faulty replaced vacuum switch or solenoid, or a faulty vacuum booster/pump.
- Check the vacuum solenoid while the engine is running. On electronically controlled EGR valves, activate the solenoid with a scan tool and check for vacuum at the end of the tube. If the solenoid does not open, is stuck in the open or closed position, or has a corroded electrical connection, loose wire, or poor ground, EGR operation will be affected. Determine root cause before replacement.
- If possible, check the valve stem movement between 1500 and 2000 rpm. The valve stem should move if the valve is working correctly – if it doesn’t, and there’s a vacuum, then there’s something wrong.
- Vacuum is applied directly to the EGR valve using either a manual vacuum pump or a scan tool depending on the type of EGR valve. If the idle quality does not change, then either the EGR valve is faulty or the passages are completely restricted. If the engine idles or stalls, a malfunction in the control system has caused the problem.
- Remove the EGR valve and check for carbon buildup. Remove carbon if possible, being careful not to contaminate the diaphragm.
- Check the manifold EGR passage for blockage and clean if necessary.
How to replace a faulty EGR valve?
- First, remove the engine cover.
- Then disconnect the electrical cable from the valve and remove the electrical connections and/or vacuum lines, checking for signs of damage.
- Remove the mounting screws and inspect the valve for damage, corrosion, or carbon build-up.
- Thoroughly clean the EGR valve mounting surface and install a new valve and gasket. Remove any loose carbon from the EGR supply port as well.
- Connect the EGR valve to the bolt holes and gasket and reattach to the housing.
- Tighten all fasteners to the recommended torque settings.
- Once securely installed, reconnect the vacuum lines and/or electrical connections.
- Finally, use the diagnostic scan tool to reset the check engine light and check for other errors. Check that the malfunction indicator is cleared and then do a road test. Many vehicles now require an EGR valve adjustment. This allows the ecyl to easily learn the stop position at open and closed points. Failure to do so may cause the valve to break and fall into the manifold.
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