You car may display a Check Engine Light, it may not be running correctly, or it may not pass your local emissions test. These can be a few of the common symptoms of the EGR (exhaust gas recirculation) valve failing. The EGR not only directly affects the emissions that your vehicle releases, but it can also cause more serious problems with the drivability of your vehicle. Knowing what the EGR valve does and how to diagnose it can help you to save some money by either doing the repair yourself, or at the very least it will help you to become an informed consumer.
Part 1 of 3: Understanding the purpose of the EGR valve and how it works
The EGR valve, or exhaust gas recirculation valve, is part of the emissions system of your car. It’s main purpose is to reduce the NOX (oxides of nitrogen) emissions that your engine emits. The way it does this is by recirculating exhaust gases back into the engine which stabilizes the temperature of the combustion chamber and also allows the combustion process to start all over again on that recirculated exhaust which reduces the amount of unburnt fuel in it.
There are two kinds of EGR valves, electronic and manual. The electronic version contains a solenoid which allows the computer to open and close it when needed. The manual version is opened when engine vacuum is applied to it and then when the vacuum it released it closes. No matter which one you have, the operation of the system is the same. The vehicle's computer will command the opening and the closing of the EGR valve depending on the vehicle speed and the engine temperature.
On most vehicles the EGR valve will only be applied when the engine is at normal operating temperature and the vehicle is moving at highway speeds. When the system is not working properly it can cause something as simple as the Check Engine Light to come on, to as serious as a stalling condition.
Part 2 of 3: Diagnosing a failing EGR valve
The EGR valve can fail for any number of reasons. When it does it can cause a number of symptoms. When an EGR valve fails it usually fails in one of two ways: it either gets stuck open or stuck closed. These symptoms can be very similar to other problems with the vehicle, so proper diagnosis is imperative.
Check Engine Light is on: When an EGR valve fails it can cause the Check Engine Light to come on. If the light is on then the computer needs to be scanned for codes. If there is a code for EGR low flow then that means that the EGR valve is not opening.
The computer can tell if the EGR valve is opening by changes it see in the oxygen sensors when the valve is open. You may also get a code for incorrect voltage for an electronic EGR valve which can indicate a circuit issue or a valve failure. A lean code can also come up if the EGR valve is stuck open. If the EGR valve is stuck open it will allow unmetered air to enter the engine which causes the computer to see too much air in the engine.
Rough idle: If the EGR valve is stuck open then that will result in a vacuum leak. That will cause the engine to run rough at idle because the excessive air cannot be properly detected by the computer.
If any of these symptoms occur you would need to diagnose the valve. Depending on the type of vehicle that it is will determine how it is tested.
No/low EGR flow code: This means that there is not enough flow of exhaust gases into the engine when the EGR valve is commanded open.This can be caused by a number of things. Being able to diagnose each one will assist in finding the problem.
Electronic EGR valve: An electronic EGR valve can go bad or have a failure in its control circuit. The best way to diagnose it is with a scan tool first. With the engine running the EGR valve can be commanded open and closed and you can watch for proper operation. If it is not working then the EGR valve needs to be tested with an Ohm meter. If the valve tests bad then it will need to be replaced. If it tests good then the circuit will need to be tested with a voltage meter.
Manual EGR valve: A manual EGR valve can fail or its control solenoid or circuit can fail. The EGR valve can be tested with a vacuum pump to see if it is stuck closed. With the engine running, you can use a vacuum pump to apply vacuum to the EGR valve. If the engine idle changes when vacuum is applied then the valve is good. If not then it needs to be replaced. If the EGR valve is fine then its control circuit and solenoid would need to be tested.
Clogged EGR passages: The EGR valve can also be good when you get a flow problem code. It is common for the EGR passages that connect the exhaust to the intake to become clogged with carbon build up. Typically the EGR valve can be removed and the passages can be checked for build up. If there is build up then that would need to be removed first and the vehicle retested.
If the issue with the vehicle is a lean code or an idle problem then that indicates that the valve is not closing. The valve would need to be removed and checked to see if the internal components mover freely. If not then it needs to be replaced.
Part 3 of 3: Replacing the EGR valve
Once it has been determined that the valve is bad then it needs to be replaced.
Step 1: Park your car on a flat surface. Park on a level surface and apply the parking brake. Allow the engine to cool down.
Step 2: Locate the EGR valve. The EGR valve is typically located on the intake manifold. The emissions sticker under the hood can assist you in locating the valve.
Step 3: Loosen the exhaust tube. Using the adjustable wrench loosen the exhaust tube that is attached to the EGR valve.
Step 4: Remove the bolts. Using the ratchet and the appropriate socket remove the bolts that attach the valve to the intake manifold and remove the valve.
Step 5: Install the new valve. Install the new valve in the reverse order and torque its mounting bolts to manufacturer's specifications.
Once you install the new EGR valve it can be retested. If checking and replacing the EGR valve seems to be too difficult for you then you should get come assistance from a certified mechanic that can change your EGR valve for you.
This article originally appeared on YourMechanic.com as How to Replace an Exhaust Gas Recirculation (EGR) Valve and was authored by Robert Tomashek.