What is EGR? How do they work? What kind of malfunctions do they have?
Integrated into the vehicle's engine management system, the aptly named exhaust gas recirculation valve, or EGR valve for short, recirculates precisely metered amounts of exhaust gas into the engine intake system for higher engine efficiency, lower fuel consumption and lower NOx emissions. With increasing pressures to reduce emissions, the EGR valve will play an increasingly important role moving forward. It's important to know what it does, why it fails, and how to replace it when it fails.
How EGR Valve Works
Examples of harsh environments for EGR valves. Approximately 80 percent of the air we breathe is nitrogen. However, when exposed to extremely high temperatures in the combustion chamber plus 1370°C, the normally inert gas becomes reactive and forms harmful oxides of nitrogen, or NOx,
which then pass through the exhaust system into the atmosphere. To help minimize this, the EGR
valve effectively changes the chemical makeup of the air entering the engine, allowing a certain amount of exhaust gas to re-enter the system. With less oxygen, the now diluted mixture burns more slowly, lowering temperatures in the combustion chamber by almost 150°C and reducing NOx production for a cleaner, more efficient exhaust.
The EGR valve has two main settings: on and off, but the position can vary anywhere in between. The EGR valve is closed when the engine is started. 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, as more torque and power are required, for example during full acceleration, the EGR valve closes to allow more oxygen into the cylinder. In addition to reducing NOx, EGR valves can be used in downsized GDi engines to reduce pump losses and improve both combustion efficiency and knock tolerance. On diesel, it can also help reduce diesel knock at idle.
EGR valve types
Although there are several types of EGR valves – earlier systems used a vacuum-operated valve, while newer vehicles are electronically controlled – the main types can be broadly summarized as: Diesel high-pressure EGR valves divert high-flow, high-soot exhaust gas before it enters the diesel particulate filter - soot can combine with oil vapor to form sludge. The gas is then returned to the intake manifold either through a pipe or internal vents in the cylinder head. A secondary valve is also used to help create a vacuum in the intake manifold, as this is not naturally present in diesel engines.
Diesel Low pressure EGR valves redirect 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 returned to the inlet manifold via a pipe. Petrol EGR valves redirect exhaust gases like their high-pressure diesel equivalent. The vacuum created by cylinder collapse draws the exhaust gases in, and the flow is regulated by the opening and closing of the EGR valve itself. Vacuum-operated EGR valves use a vacuum solenoid to vary the vacuum relative to the diaphragm and sequentially turn the EGR on and off. Some valves also include a feedback sensor to inform the ECU about 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 regulate exhaust gas flow.
Why do EGR valves fail?
EGR valves operate in a hostile environment, so they will experience wear and tear over time. However, the single biggest cause of failure is the buildup of carbon particles from the exhaust gases along the EGR and intake system passages. Over time, this clogs the tubes, exhaust gas passages, and eventually the valve's piston mechanism, causing the valve to remain open or closed. Malfunctions can also be caused by a tear or leak in the valve diaphragm. What to look for in a faulty EGR valve?
The symptoms associated with EGR valve failure are similar to those of many other engine management components, and that is why EGR malfunctions continue to be a source of headaches for many technicians. However, there are a few signs to look out for:
Check engine light: Like most engine management components, a problem with the EGR valve can trigger the check engine light.
Engine performance problems: If the valve remains open, the vehicle's air-fuel ratio will be disrupted, causing engine performance problems such as loss of power, poor acceleration, and rough idling. It can also produce turbo boost pressure leaks, causing the turbo to work harder.
Increased NOx emissions: When the EGR valve remains closed, the resulting high temperatures in the combustion chamber leave too much unburned fuel in the exhaust, causing increased NOx emissions and reduced fuel efficiency.
Engine knocking: Higher temperatures and NOx can also cause increased engine knocking or knocking, heard as knocking noises.
Troubleshooting the EGR valve
Considering the different types of EGR valves, it is always best to follow the troubleshooting procedures detailed in the service manual, but there are a few general steps that can help pinpoint the diagnosis:
Read fault codes on electronically controlled EGR valves using a diagnostic tool.
Check that all vacuum lines and electrical connections are correctly connected and located.
Use a vacuum gauge to check the vacuum supply hose for vacuum at 2000 to 2500 rpm. No vacuum at normal operating temperatures does not indicate a loose hose, a clogged or faulty vacuum switch or solenoid, or a faulty vacuum amplifier/pump.
Check the vacuum solenoid with the engine running. On electronically controlled EGR valves, activate the solenoid with a scan tool and check for vacuum at the end of the pipe. If the solenoid does not open when powered up, remains stuck in the open or closed position, or if the electrical connection is corroded, the cable is loose, or the ground is poor, EGR operation will be affected. Determine the root cause before replacement.
If possible, check valve stem movement at 1500 to 2000 rpm. If the valve is working properly the valve stem should move - if not and there is vacuum, there is a fault.
Apply vacuum directly to the EGR valve using a hand vacuum pump or scan tool, depending on the type of EGR valve. If there is no change in idle quality, either the EGR valve is faulty or the passages are completely restricted. If the engine idles rough or stalls, a malfunctioning control system is causing the problem.
Remove the EGR valve and check for carbon buildup. If possible, remove the carbon, being careful not to contaminate the diaphragm.
Inspect the EGR passage in the manifold for obstruction and clean if necessary.
Common EGR fault codes The following fault codes are common on newer model EGR valves:
P0400: EGR flow malfunction
P0401: EGR insufficient flow detected
P0402: EGR overflow 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 needle error
P1405: EGR solenoid high
P1406: EGR system pintle position error
How to replace a faulty EGR valve?
First remove the engine cover.
Then loosen the electrical wire on the valve and check for signs of damage by disconnecting the electrical connections and/or vacuum lines.
Remove the fixing screws and check the valve for damage, corrosion or carbon build-up.
Clean the EGR valve mounting surface thoroughly and install the new valve and gasket. Also remove any loose carbon from the EGR feed port.
Align the EGR valve with the bolt holes and gasket and reinstall it into the housing.
Tighten all fasteners to recommended torque settings.
Once secure, reconnect vacuum lines and/or electrical connections.
Finally, use a diagnostic scan tool to reset the check engine light and check for other faults. Check that the malfunction indicator light goes out, then perform a road test. Many vehicles now require the EGR valve to be reset under retrofits. This allows the ECU to learn the stop position at open and close points. Failure to do so may cause the valve to break and fall into the manifold.
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