Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.
Learning how to test an EGR valve will save you time, money and some headaches. After miles of service, the exhaust gas recirculation EGR system—especially the EGR valve—will lead to engine performance problems due to carbon buildup, components mechanical problems, or vacuum hose leaks. Depending on the particular problem, you'll notice symptoms like rough idle, pinging or knocking engine sounds, an increase in emissions, poor fuel economy, hard starting and even stalling. Without some troubleshooting, though, these same symptoms will mislead you into replacing an otherwise good EGR valve, solenoid, or miss a simple solution to your problem.
Here, we take a look at a simple procedure to troubleshoot a potential bad EGR valve, and a few tips to do some system cleaning, if necessary.Lexus ls400 fuse boxes
In either case, I'd recommend you buy the vehicle repair manual for your particular make and model, if you don't have one yet. The manual will help as a reference, either now or later, to identify the exact type and components you have in your EGR system; help you in identifying passageways for cleaning the system, including the valve itself; and the correct steps if you need to replace the EGR valve. Not to mention all the help you'll get in future maintenance and repairs for your vehicle.
You can get fairly inexpensive aftermarket repair manuals from most auto parts stores or online. Or, if you don't want to buy the manual now, look up a copy of the manual in the reference section of your local public library.
And one more thing. Here, we'll deal with vacuum controlled EGR valves found in old model vehicles and some newer models using hybrid vacuum-electronic controls.
New vehicle models come with electronically controlled valves, though about six different types of EGR-valve control configurations exist today, and some late model cars have rid of the EGR valve entirely. Still, you can follow this guide along with the procedure described in your vehicle manual to test your EGR valve, if necessary. To apply one of the tests to the EGR valve, you'll need a vacuum pump, which you can borrow-rent from a local auto parts store, if you don't have one.
Other than that, you'll only need to use some common tools if you need to clean carbon buildup from EGR system passages. The EGR system in your vehicle uses the EGR valve to introduce measured amounts of exhaust gases back into the combustion chambers.
These gases lower combustion temperatures. And lower combustion temperatures mean lower emission of harmful NOx oxides of nitrogen gases. However, exhaust gases shouldn't flow continuously into the cylinders.Sort results: alphabetical rank? Menu Search.
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But if the EGR system is leaking or inoperative, it can cause driveability problems, including detonation knocking or pinging when accelerating or under loada rough idle, stalling, hard starting, elevated NOx emissions and even elevated hydrocarbon HC emissions in the exhaust.
Exhaust gas recirculation reduces the formation of NOX by allowing a small amount of exhaust gas to "leak" into the intake manifold. This keeps combustion temperatures below degrees C degrees F to reduce the reaction between nitrogen and oxygen that forms NOx.
To recirculate exhaust back into the intake manifold, a small calibrated "leak" or passageway is created between the intake and exhaust manifolds. Intake vacuum in the intake manifold sucks exhaust back into the engine. But the amount of recirculation has to be closely controlled otherwise it can have the same effect on idle quality, engine performance and driveability as a huge vacuum leak.
The EGR valve remains closed until the engine is warm and is operating under load. As the load increases and combustion temperatures start to rise, the EGR valve opens and starts to leak exhaust back into the intake manifold.
This has a quenching effect that lowers combustion temperatures and reduces the formation of NOx. These include increasing camshaft valve overlap, redesigning the combustion chamber and modifying ignition advance curves. Three-way catalytic converters also reduce NOx in the exhaust.
If the EGR system is rendered inoperative because it was disconnected or tampered with, the cooling effect that was formerly provided by the EGR system will be lost. Without EGR, the engine will often knock and ping detonate when accelerating or lugging the engine. This can cause engine damage over time.Universal rundle tub stems
The typical ported vacuum EGR valve consists of a vacuum diaphragm connected to a poppet or tapered stem flow control valve. The EGR valve itself is usually mounted either on a spacer under the carburetor or on the intake manifold. A small pipe from the exhaust manifold or an internal crossover passage in the cylinder head and intake manifold routes exhaust to the valve. When vacuum is applied to the EGR valve, it opens. This allows intake vacuum to suck exhaust into the engine. To prevent the EGR valve from opening when the engine is cold, the vacuum line to the EGR valve may be connected to a parted vacuum switch or a computer-controlled solenoid.
Vacuum is not allowed to pass to the valve until the engine is warm. EGR isn't needed when the engine is cold, only when it is warm and under load. Backpressure EGR valves use exhaust backpressure to vary the point at which they open and their flow rates. On GM cars, they are identified by the last letter on the part number on top of the valve. A letter "P" indicates a positive backpressure valve, and a letter "N" indicates a negative backpressure valve.
Inside a backpressure EGR valve is a second diaphragm that reacts to backpressure in the exhaust system. The backpressure diaphragm opens and closes a small bleed hole in the main EGR vacuum circuit or diaphragm chamber.
Opening the bleed hole reduces vacuum to the main diaphragm and prevents the valve from opening fully. Closing the bleed hole allows full vacuum to reach the main diaphragm so the valve can open wide and allow maximum EGR flow.
This reduces backpressure somewhat, allowing the backpressure diaphragm to bleed off some control vacuum. The EGR valve begins to close and exhaust pressure rises again.
The EGR valve oscillates open and closed with changing exhaust pressure to maintain a sort of balanced flow. The negative backpressure type of EGR valve reacts in the same way, except that it reacts to negative or decreasing pressure changes in the exhaust system to regulate EGR action.
A drop in backpressure occurs when there is less load on the engine. This causes the backpressure diaphragm to open a bleed hole and reduce EGR flow. It's the same principle as with the positive type except that the control function occurs when backpressure goes down instead of up. The engine must be relatively warm before it can handle EGR.It has to do with the emissions system and stands for:. The EGR system on a vehicle is responsible for recirculating exhaust gasses in order to lower the vehicles emissions output.
Related: P Ford Explorer. Most of the time there are not going to be symptoms when P is triggered, other than the service engine soon light itself.Supertest timeout
In some extreme cases, you may notice a slight ping or knock. Diagnosing what is causing the P code in the Explorer is typically not very tricky. Here are the most common causes:. The good news with P is that it rarely ever costs much money to fix, and it is usually pretty easy to get the problem, since it is right on top of the engine. That can be a mistake. Here are some of the most common fixes to help clear the P Testing your EGR system is relatively easy to do.
P0401 FORD - Exhaust Gas Recirculation Flow Insufficient Detected
The most challenging aspect is the DPFE sensor. By process of elimination, you can be relatively confident that the DPFE is at fault. If there is anything you would like to add about P, please feel free to add a comment below. Good luck!! Related: P Ford Explorer Ford Explorer P Symptoms Most of the time there are not going to be symptoms when P is triggered, other than the service engine soon light itself. Service Engine Soon Light — P will illuminate the service engine soon light.
Knocking Sound — In certain cases, there may be a noticeable knock that comes from the vehicle.
How to Test an EGR Valve: A Simple Procedure
Here are the most common causes: Blocked EGR Tube — The tube that carries the exhaust gases back to the motor may clog up over time. Alternatively, it can become bent or kinked.
This is especially true if you are experiencing P right after doing some engine work. Check the tube and see if it is cracked, clogged or otherwise damaged.
But, they certainly are the cause of P often enough. So, if you are encountering P and other codes, the P may be a symptom of larger problems. For instance, if the motor is not running well enough to create sufficient vacuum to operate the EGR valve, than P will often be thrown.
Explorer P Fix The good news with P is that it rarely ever costs much money to fix, and it is usually pretty easy to get the problem, since it is right on top of the engine. Conclusion Testing your EGR system is relatively easy to do.On some vehicles, the OBD II system may monitor the operation of the exhaust gas recirculation system. NOX emissions are highest when the engine is under load, which means you may not be able to get accurate readings unless the vehicle is tested in a "loaded mode" by driving it on a dyno, or using a portable exhaust analyzer while test driving the vehicle on the road.
Exhaust gas recirculation is only a part-time function. It should NOT occur when the engine is cold because it acts like a vacuum leak and can cause a rough idle or lean misfire. It should only occur after the engine has warmed up and is running at a speed above idle. The EGR valve should be fully closed when the engine is off. If it is not, it can make for hard starting when the engine is cranked. If teh engine has a vacuum-operated EGR valve, the PCM controls a solenoid in the vacuum line to open and close the valve.
Inceasing the "on time" of the solenoid holds the valve open longer and increases the flow rate. Each has a different sized valve small, medium and large. The PCM varies the flow rate by energizing various combinations of the solenoids. The solenoids are normally closed, and open only when the PCM completes the ground to each. The further the valve opens, the greater the flow rate. The EVP sensor also helps with self-diagnostics because the computer looks for an indication of movement from the sensor when the it commands the EGR valve to open or close.
The sensor works like a throttle position sensor and changes resistance. The voltage signal typically varies from 0. When the computer commands the EGR valve to open, it wants to see a movement signal from the EVP sensor within a certain number of milliseconds typically 50 ms or less.
Exhaust Gas Recirculation (EGR)
But as the EGR valve ages, it may not open as quickly as it once did. It still works and keeps NOX emissions within acceptable limits, but the computer thinks the EGR valve is not opening quickly enough and sets a code.
This requires a Tech 2 scan tool and a software update from GM. Most scan tools can access a menu called "Mode When you go to the Mode 06 menu, you can see the OBD II self-test data for all the EGR components and can tell at a glance whether they are operating in or out of range. See the Mode 06 Diagnostics section for more info. Pinging spark knock or detonation because the EGR system is not working, the exhaust port is plugged up with carbon, or the EGR valve has been disabled.
The fix here is to inspect the EGR system, remove the EGR valve and check the valve and port for carbon, and remove the carbon from the port if it is plugged. Rough idle or misfiring because the EGR valve is not closing and is leaking exhaust into the intake manifold.
You may also find a P "random misfire" code. The fix here is to connect a vacuum gauge to the intake manifold and check intake vacuum at idle. A normal reading is typically 17 to 22 inches Hg. IF the reading is low, it indicates a vacuum leak. Check all vacuum hose connections for loose or disconnected hoses. Replace any hoses that are cracked. If there are no obvious vacuum leaks, remove and inspect the EGR valve.
Look for carbon buildup on the EGR valve or the seat that would prevent it from closing. Clean as needed. IF teh EGR valve is stuck open or is damaged, replace it. Hard starting because the EGR valve is not closing and is creating a vacuum leak into the intake manifold.Phenylthiocarbamide tastingalso called PTC tastinga genetically controlled ability to taste phenylthiocarbamide PTC and a number of related substances, all of which have some antithyroid activity.
PTC-tasting ability is a simple genetic trait governed by a pair of alleles, dominant T for tasting and recessive t for nontasting. Persons with genotypes TT and Tt are tasters, and persons with genotype tt are nontasters; there appears to be hormonal mediation of the tasting ability, however, because women are more often taste-sensitive in this regard than are men.
It has been suggested that PTC tasting may be related to the genetically determined level of dithiotyrosine in the saliva. PTC-tasting ability is not particularly useful, it would seem, since PTC does not occur in food, but some substances related to PTC do occur in food items. As for the utility of being able to taste PTC, it appears that nontasters of PTC may have a higher than average rate of goitre, a disease of the thyroid gland sometimes associated with a lack of iodine; because PTC and related compounds contain iodine, there may be a selective advantage of some kind for tasters or nontasters in different environments.
It has also been suggested that tasters may have more food aversions than nontasters, a disadvantage in situations of food scarcity. The chief reason for interest in tasting ability, however, is that the frequency of tasters varies from population to population. Phenylthiocarbamide tasting. Info Print Cite. Submit Feedback. Thank you for your feedback. Phenylthiocarbamide tasting biology.
See Article History. Learn More in these related Britannica articles:. Taste blindness for PTC and other carbamides appears to be hereditary as a recessive traitoccurring in about a third of Europeans and in roughly 40 percent of the people in Western India. Taste blindness for carbamides is not correlated with insensitivity to….
History at your fingertips. Sign up here to see what happened On This Dayevery day in your inbox! Email address. By signing up, you agree to our Privacy Notice. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. More About. University of Washington - Phenylthiocarbamide.In the early s, automobile manufacturers began equipping their vehicles with EGR exhaust gas recirculation valves to reduce the levels of pollutants created by their vehicles.
At high temperatures, oxygen and nitrogen combine to form nitrogen oxide, which is considered one of the main components of smog.Sanyo tv main board
EGR valves help to reduce the amount of nitrogen oxide produced by automobile engines by lowering the temperature of the combustion process in an engine. Nitrogen oxide is a noxious gas and is one of the main components found in smog. It is produced during the combustion process in an automobile when temperatures in the combustion chamber exceed 2, degrees. The EGR valve works to lower the combustion temperatures in an engine by introducing a controlled amount of exhaust gases into the engine cylinders.
These exhaust gases cannot be burned again and merge with the fuel and air mixture that enters into a cylinder, which chemically lowers the temperature at which the fuel and air mixture burns, reducing the production of nitrogen oxides. The EGR valve has an inlet tube that is connected to the engine's exhaust system and an outlet tube that is connected to the intake manifold.
The main body of the unit contains a valve which opens under certain conditions to allow a certain amount of exhaust gas into the intake manifold, where it then mixes with the fuel and air mixture and cools the combustion process.
EGR valves on older vehicles manufactured before are operated according to the amount of vacuum created by the engine under different operating conditions. These units have a vacuum hose attached to them which connects to the intake manifold and provides the ported vacuum necessary to operate the valve. As the throttle is opened more vacuum is created, which causes the valve to open and introduce exhaust gases into the intake manifold. These early EGR systems also used a thermal switch which prevented the vacuum from operating the EGR valve until the engine reached normal operating temperature.
Newer vehicles manufactured after use vacuum and electronic signals to control the operation of the EGR valve. The EGR valve is connected to a vacuum source from the engine and also has one or more wires connecting it to the vehicle's computer. The computer uses sensors to monitor the operation of the engine and sends signals to solenoids within the EGR valve to more precisely control the valve's operation than vacuum operation alone can. This allows the EGR valve to operate much more efficiently and further reduce the production of nitrogen oxides.
When EGR valves fail, the system is unable to properly introduce exhaust gases into the fuel and air mixture, which causes the temperature within the combustion chambers to increase.Whenchat ios
This temperature increase can cause pre-ignition, knocking and pinging, and over-production of nitrogen oxide. To prevent this, modern vehicles use computer controls which note when the EGR valve is no longer adding exhaust gases to the fuel and air mixtures.
The computer then reduces the amount of ignition advance, which in turn slows down the combustion process, but at the cost of reducing performance and fuel mileage. When the EGR valve fails, a code is set in the vehicle's computer, which causes the check engine light to come on. This code also allows automobile technicians to quickly determine the cause of the problem. This article was written by the It Still Works team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information.
To submit your questions or ideas, or to simply learn more about It Still Works, contact us. Vacuum Control EGR valves on older vehicles manufactured before are operated according to the amount of vacuum created by the engine under different operating conditions. Electronic Control Newer vehicles manufactured after use vacuum and electronic signals to control the operation of the EGR valve.
EGR Failure When EGR valves fail, the system is unable to properly introduce exhaust gases into the fuel and air mixture, which causes the temperature within the combustion chambers to increase. About the Author This article was written by the It Still Works team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information.
Photo Credits the powerful engine image by kuhar from Fotolia.
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