will cleaning the throttle body help stop pinging 03 mazda protege lx

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

Has your EGR valve (your Exhaust Gas Recirculation valve) gone bad? Maybe. I'll tell you the symptoms below. But before you start replacing parts, keep in mind that the same engine performance problems that indicate a bad EGR valve can also indicate problems in other parts of the system. If you don't do your troubleshooting, you may end up replacing parts unnecessarily and wasting time and money.

This article will tell you several things:

the symptoms of a bad EGR valve;
how to start investigating whether the problem is your EGR valve or something else;
what the EGR valve does and how it works;
and the different types of EGR valves.

EGR valve passages plugged with carbon deposits.

Photo courtesy of Moosealope on Flickr

Symptoms of a Bad EGR Valve

Symptoms of a bad EGR valve include:

rough idling or stalling
a smell of fuel
increased fuel consumption
pinging, tapping, or knocking sounds
failed smog test
Check Engine Light on

Another symptom you may not see often is a misfire. The misfire is actually caused by clogged passages in the intake manifold.

Carbon buildup from exhaust gases flowing through the EGR valve may restrict flow to one or more cylinders. The rest of the cylinders then will get all the exhaust flow, leading to the misfire.

The intake ports and EGR valve itself may also have carbon deposits. All these passages and ports will need to be cleared.

Valve Stuck Open vs. Valve Stuck Shut

Actually there are two kinds of bad EGR valves, with different symptoms. An EGR valve can fail in two ways: It can be open all the time, or it can be closed all the time.

If the EGR Valve Sticks Open:

This will cause a continuous flow of exhaust gases into the intake manifold. You'll notice one or more of the following symptoms:

A rough idle upon starting the engine (that is, when the engine is cold) and sometimes at a stop light or while looking for a spot in a parking lot (that is, at low engine speeds in a warmed-up engine).
Stalling when the engine idles.
Increase in fuel consumption.
A slight—or strong—fuel odor while operating the vehicle, because of the increase in hydrocarbons leaving the tailpipe (see the next symptom).
Your car fails the emissions test. When the engine is running at low RPM, lower temperatures in the combustion chambers prevent all the fuel from burning, so the flow of unburned hydrocarbon gases coming out of the tailpipe increases significantly.
The Check Engine light (or Malfunction Indicator Light, MIL, depending on your model) illuminates on your dashboard.
You feel the engine has low power, especially at low speeds.

If the EGR Valve Sticks Closed:

This will permanently block the flow of exhaust gases into the intake manifold. You'll notice one or more of the following symptoms:

A pinging or tapping noise coming from the engine at low RPM (at speeds higher than idle). The noise is the sound of early ignition of the fuel when it meets high temperatures.
Loud detonations. A second ignition can happen after the normal ignition, and the two can combine with enough power to cause engine damage.
Your car fails the emission test. High temperatures in the combustion chamber allow the excessive formation of oxides of nitrogen, which are released through the tailpipe.
The Check Engine light, or Malfunction Indicator Light (MIL), illuminates on your dashboard.

Troubleshooting: Is It the EGR Valve or Something Else?

To make things even more complicated, the same engine performance problems that indicate a bad EGR valve can also indicate problems in other parts of the system:

The EGR's Job: Processing Exhaust Gases

The outside air picked up through the engine's intake manifold contains close to 80 percent nitrogen and 20 percent oxygen, along with small amounts of other elements. When outside air combines with the fuel and ignites in the combustion chamber, temperatures can reach above 2500^o F (or 1370^o C). Combustion at these temperatures burns the usually inert gas nitrogen, creating oxides of nitrogen (NOx) gases, which cause air pollution and human health problems.

However, when the burned exhaust gases are introduced back into the combustion chamber through the EGR valve, temperatures decrease, inhibiting the formation of NOx gases.

What the EGR Valve Does

The EGR valve is a small component designed to allow the flow of exhaust gases into the intake manifold in controlled amounts. As such, it's a simple valve that closes and opens as needed.

The EGR valve has one single job to do, regardless of the system configuration, type of control and number of sensors: that is, to either open and direct exhaust gases into the combustion chamber, or to close and keep them from entering.

Whenever you start the engine, the valve comes alive and waits in a closed position, blocking the flow of exhaust gases.

Once the engine reaches operating temperature and speed increases, the valve—either through vacuum or electronic control—gradually opens, allowing burned exhaust gases to enter and combine with the air-fuel mixture inside the combustion chamber. If you slow down sufficiently or come to a stop, the valve gradually closes and blocks the flow of exhaust gasses. And the process continues for as long as the engine is running.

After you shut off the engine, the EGR valve closes and remains in that position.

Types of EGR Systems

Gasoline and diesel-powered engines on the road today may use one of several different EGR valve configurations.

On older vehicle models, you'll recognize the EGR valve as a round, thick metal disc about three inches in diameter, usually towards the top of the engine and on the side. On these older models, a small-diameter vacuum hose operates a basic EGR valve. The hose connects the top of the valve to the throttle body or carburetor. The valve's metal disk houses a vacuum diaphragm, spring, and plunger.
Later models come equipped with electronic-vacuum EGR valves inside a small block or cylinder. The valve works the same way as in older models, except that an electronic EGR position sensor communicates with the car's computer for better control. You may see electric solenoids connected through vacuum lines to the valve as well.
Newer vehicle models use electronic EGR systems that may include additional components, even a digital valve that eliminates the need for vacuum control altogether.
A more radical design, implemented in a few models, was the replacement of the valve with EGR jets at the bottom of the intake manifold.
Some newer high-efficiency engines, for example those with variable valve timing (VVT), don't even use an EGR system.

Types of EGR Valves

Vacuum-controlled EGR valve
Back-pressure EGR valve
Electronic vacuum-controlled EGR valve
Digital EGR valve
EGR jet (in place of EGR valve)

Locating the EGR on a Corvette and on a Truck

Bad EGR valve symptoms vary and resemble problems in other engine systems. But now that you know the type of symptoms a troubled EGR valve will produce, include it in your troubleshooting tests. And restrain yourself from swapping components trying to fix the problem before knowing which part is causing you trouble. Most of the time, you'll just spend time and money unnecessarily. Troubleshoot your EGR valve and other components.

Test Your Knowledge

For each question, choose the best answer. The answer key is below.

Which condition does NOT point to a potentially failed EGR valve?
- Excessive oxides of nitrogen
- Excessive hydrocarbon
- Excessive hydrocarbon and carbon monoxide
Which of these is NOT a symptom of an EGR valve stuck open?
- Rough idle and stalling
- A smell of fuel
- High oxides of nitrogen (NOX) results on emissions test
Which of these is NOT a symptom of an EGR valve stuck closed?
- Pinging or tapping
- Loud detonations
- High hydrocarbon (HC) results on emissions test
What else, besides an EGR valve stuck open, can cause high hydrocarbon emissions?
- Bad oxygen sensor
- Warped rotors
- Transmission fluid leak

Answer Key

Excessive hydrocarbon and carbon monoxide
High oxides of nitrogen (NOX) results on emissions test
High hydrocarbon (HC) results on emissions test
Bad oxygen sensor

This content is accurate and true to the best of the author's knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

Questions & Answers

Question: I have had my EGR valve cleaned and then replaced in my 2002 Ford Tauras which has 49,000 miles. Now it idles rough and the check engine light came back on. What could be the issue?

Answer: If the trouble codes point to the EGR, then there's possibly something wrong in the system. It depends on the codes. Make sure the circuits (wiring) are checked as well.

Question: Why would the EGR valve leak oil?

Answer: The oil may come through a seal from the actuator rod which somehow connects to the crankcase ventilation (CCV) system. This seems to be a recurrent problem on some models. You may try replacing the EGR valve and see if the problem doesn't return.

Question: I have a Hino 2011 268, and the SCR malfunction light turns on and off. What is wrong?

Answer: There could be an intermittent problem with the SCR system. You may be able to get the codes. This video may give you an idea of how to get the codes yourself:

https://www.youtube.com/watch?v=VLf3dgDlLoY.

Question: If I have a bad EGR valve, will it throw a code for a misfire in cylinder number 2?

Answer: A bad valve most likely will cause a random misfire since it doesn't direct exhaust gases to a particular cylinder. If you are getting a code for the number 2 cylinder, check the injector, spark, or fuel problems for that cylinder.

Question: Can a bad EGR valve cause my vehicle to buck on acceleration and then stall out?

Answer: There could be several reasons for this, clogging fuel filter, problems with the ignition system or fuel system.

Question: My '96 Tahoe develops a front to rear jerking coming from the engine bay at highway speeds and under constant speed, not accelerating or decelerating. When I unplug the EGR wiring dongle the problem disappears. Any thoughts on this?

Answer: The EGR valve may be getting stuck from carbon build up. The jerking you are feeling is probably a vacuum leak. More air entering the engine is upsetting the amount of fuel the computer think it really needs. Check the valve and passages for carbon buildup. Probably other components in the system may be causing this too.

Question: Where is the EGR located on a 2003 Nissan Maxima?

Answer: If your model has the valve, look under the air cleaner assembly boot where it connects to the throttle. You should see a black round component (looking from the top) with an electrical connector on the side.

Question: I have a 1996 Acura and the trouble code reading was for the EGR valve. Will a bad EGR valve cause white smoke? The car drives fine and a light smoke comes only when I'm at a red light. And then take off I can see thin white smoke. What does white smoke mean?

Answer: Usually, white smoke is associated with coolant leaking into the exhaust stream, while black smoke is oil getting into the cylinders from a bad piston ring, faulty valve seals or PCV system. This other post may help:

https://axleaddict.com/auto-repair/Exhaust-Color-S...

Question: Do you need to remove the EGR valve when replacing the cylinder head?

Answer: The EGR valve connects to the cylinder head. Depending on the particular setup for your model, it may be possible to remove the head along with the valve. Other times, you may need to remove it before removing the head.

Question: I have a 2016 Nissan Navara NP300. Is it advisable to block the EGR. I have heard that it is advisable to do so to prevent engine damage. What is your opinion?

Answer: The EGR prevents the engine from overheating and forming NOx emissions (very toxic). So it's better not to block it.

Question: In an 2013 Audi A3, could the EGR valve be the cause of the loss of coolant consistently?

Answer: If your particular valve uses coolant to check for a possible leak. I don't know how accessible the valve is in your particular model. You may need the repair manual if you want to inspect it your self.

Question: Ford Focus Zetec 1.8L TDCI/MAN. Got engine fault. Test did not pass due to EGR not working properly. The battery goes flat when EGR socket connection is connected. (I removed this connection and battery is OK now). Engine revs up at top speeds 60-80 Kms/hr. with a deep sound and EGR disconnected. Power very low, temperature quite high although was Summer. Do you think I may need to replace the EGR?

Answer: It's better to replace the EGR and have the system operating as it should. Some car owners like to block the system, but higher temperature may lead to other problems later on.

Question:

I hear a sucking noise in my car engine. What does this mean?

Answer: Maybe this post can help:

https://hubpages.com/auto-repair/How-to-Find-and-F...

Question: Can a vehicle lose power if the EGR valve is bad?

Answer: Yes, it's possible.

Question: I own an Ashok Leyland EGR system 1618T. I have changed the EGR three times, and again it is defective. This is the fourth time. The EGR is leaking from inside. What are the possible causes?

Answer: The system uses a simple (but different) iEGR design that's able to accommodate up to 400 HP. If there's no visible outside leak into the valve, you might want to contact the dealer and refer the issue to them.

Question: I have a 2009 Dodge Grand Caravan 4.0 L. It cranks but will not start occasionally. It will smell gas when this happens. I have changed the WIN Module/Cam and Crank Sensors, but there is no code in the computer's memory. Can an EGR valve stop my Dodge Caravan from starting?

Answer: The smell of gas seems suspicious. Too much gasoline is probably flooding the engine. You might want to check the fuel injectors (possibly leaking) and fuel pressure. This post may help you:

https://axleaddict.com/auto-repair/How-to-Test-a-F...

Question: I have a 05' Subaru with 2.5. Whenever pumping gas, the car would stall or wouldn't restart unless I held the gas pedal to the floor. Now, the car will run fine for a minute, and then run real rough before stalling. The throttle is unresponsive. I am not finding vacuum leaks. The car has new wires, plugs, coil and fuel pump. The EGR valve seems to get very hot compared to everything else. Do you have any thoughts?

Answer: Check first for possible pending trouble codes, just in case. It's normal for the EGR valve to get hot, but if it's stuck open, it can cause the engine to stall. Also, check the throttle body for carbon build up around the bore and underneath the plate. Check the throttle position sensor. You may need your repair manual for this, but they're not difficult to inspect.

Question: Can an EGR valve pressure sensor stop your car from shifting out?

Answer: Performance wise, common bad sensor symptoms show up as engine hesitation, loss of power or even rough idle.

Question: I am getting a problem in the transmission in my Ford Ranger XLT, and the company servicing the vehicle says it's the EGR causing that problem. Does the EGR can affect the transmission?

Answer: The EGR valve affects the operation of the engine and the emission system directly. But in modern vehicles, driveability problems can affect transmission operation. The EGR system being an example of this. And many shops are aware of this issue, specially with GM and Ford models. So, it is possible the EGR system is affecting your transmission.

Question: I have replaced the EGR valve 2 times. Both time the error went straight away. And after 1000 miles, the error came back. May I know what to do now?

Answer: One common issue with EGR valve problems are carbon buildup in the intake and/or exhaust passages. Sometimes, carbon builds up deeper into the intake manifold and cause trouble. Check also the wiring and vacuum hoses (if applicable) that connect to the valve.

Question: I have a 2009 Ford Focus 2.0. It starts bucking between 2500 and 3000 rpms. It runs fine when the EGR valve is disconnected. I replaced it to no avail. I also cleaned the MAP sensor to no avail. The EGR seems to open and close rapidly when I have light pressure on the accelerator. There is no "check engine" light. Is something upstream causing this?

Answer: There could be a problem with the DPFE sensor; it looks something like this:

https://www.samarins.com/diagnose/sensors/dpfe-sen...

It could be a switching valve problem (vacuum supply problem).

Even if the CEL (engine light) doesn't come on, check for pending codes.

Question: I have a 1989 Buick LeSabre 3.08, and it will backfire in the intake manifold. It can also be hard to start like it's not getting gas, but once started it runs great. Could this be the EGR valve?

Answer: You might want to check this post:

https://hubpages.com/auto-repair/Engine-Backfires-...

Question: Can I test an EGR valve by compressing the diaphragm and holding my finger where the vacuum line goes to see if it holds pressure?

Answer: Yes, it is possible. Just make sure not to damage the diaphragm.

Question: I had an EGR valve fail last week with the P0404 code. I replaced the EGR valve, and it was loaded with carbon buildup. I blew the area to try to get rid of the carbon and then sprayed cleaner (carb cleaner) before putting the new part on. It drives WAY better now, but the Check Engine light just came on again a week later and now is throwing the P0420 code, Catalyst system efficiency below threshold. Could it be cat failing because of all that carbon?

Answer: Make sure this is the only code the computer is throwing; otherwise, look first into the other codes. A blocked EGR valve can cause combustion temperatures to rise, creating a lean condition and raising exhaust temperature. This prevents the cat from working properly. If the EGR issue has been fixed (intake and valve passages clear, and the temperature is back to normal), try clearing computer codes as a P0420 can be the result of the previous issue.

If that doesn't fix the problem, it's possible the cat or one or more O2 sensors are covered with carbon deposits. Sometimes a cat cleaner will do the job, but you need to check if the sensors are still working correctly. Otherwise, the problem with the cat is more serious.

Maybe this other post can help:

https://hubpages.com/auto-repair/How-to-Check-an-O...

Question: I've got the symptoms of a vacuum leak; aka high idle and no power. The car is idling at 1500 to 2000 rpm. Could the EGR cause this problem? I can not find any vacuum leaks, and the EGR is the only component that I haven't changed yet.

Answer: The EGR gasket may leak. If there are no other symptoms, the source could be somewhere else. Get the codes from the ECM first. The idle air control valve is another possibility. This one is easy to remove and check. Check all vacuum hoses with a piece of hose to listen for noises around the engine.

Question: I have a 2006 Audi A4 TDI. When I'm about 1300m above sea level, the car operates fine, but when I go to the coast, the car loses power as if the turbo stops working. I have taken it for Diagnostics with Audi. They say the EGR valve needs to be replaced. Does this sound like the cause of the problem?

Answer: The EGR system does need to have a specific calibration to respond quickly to changes in demands to the pressure level in the intake system. In this particular case, it's hard to tell if the EGR system is the one affected more by the difference in pressure, but certainly, it is possible.

Question: I just had the EGR valve and its controller replaced. I was hoping this would turn off the check engine light that goes on and off periodically. Not only did it not fix the check engine light, but now my car idles rough at stoplights and sometimes just at idle. My mechanic, when he replaced the EGR valve, said as I was leaving that it might take a little time for the valve and the idle to the light to become compatible? Do you know what he was talking about? Thank you.

Answer: I don't know what exactly he means by "for the valve in the idle to the light compatible." But, if he disconnected the battery while working on the EGR system, he might be referring to the car's computer relearning its idle and fuel trim strategy, which usually gets erased when power is disconnected. It erases data from memory.

Also, do you know if he cleared any trouble codes from the computer memory after replacing the valve? If not, you can go to a local auto parts store and ask them to pull any trouble codes (so that you can verify the code relates to the EGR system) and have them clear the memory. This could help. Also, you can wait for the computer to relearn the strategy, which may take a few miles. Or you can check your vehicle repair manual and see if it gives you the procedure to perform the idle relearn process.

Question: My car lost all power and would not start with the turn of keys. The "EGR" warning light came on the dash--does that mean that my engine needs replacing?

Answer: It could be the valve itself or something in the circuit. Get the trouble code and see if it points to the valve. Even if the valve seems to be at fault, it's a good idea to test the valve. Sometimes another related problem may make the ECU 'think' that the valve is at fault.

Question: I have a 1986 Dodge Ram D150 that's been sitting for years. I got it started today, and there's smoke coming from underneath the EGR valve. Any idea of why this is happening?

Answer: The EGR valve gasket is probably leaking, allowing exhaust fumes to escape. Remove the valve, clean buildup around the valve and passages, if any, and replace the gasket.

Question: I have a Crown Victoria that will not stay running unless my foot is on the gas, is it the EGR?

Answer: Check the idle air control (IAC) valve for proper operation or carbon buildup. You'll need to remove it and do a visual inspection of the valve, as well as the ports.

Question: I changed the plugs of my 1998 Ford f150 5.4, and then the "check engine" light checked. The shift solenoid B and EGR vacuum regulator is wrong. Could one of these codes make the truck vibrate and run like I have bad plugs?

Answer: Usually, a bad shift solenoid can cause hard shifts, cause the truck jerk when shifting, or shift erratically. Often, a bad EGR vacuum regulator can affect power and increase emissions.

Question: I have replaced the starter, alternator, fuel pump, spark plugs and wires on my 1998 Jeep Grand Cherokee, but it still won't start or it dies when it does. What else should I do?

Answer: Check the fuel pressure and compare it to specs. You'll need the repair manual for your model.

Question: My 98 Lexus ES300 has codes po001/po004, can the EGR set off those codes?

Answer: The description for these codes point to the electrical circuit that connects the fuel pressure regulator to the car computer.

Check first for proper connections and corrosion, a leak on the pressure regulator or failing pump.

If the fuel rail on your engine has a fuel shut-off, check that one too.

Question: Why is my car making a whining noise after I changed the EGR?

Answer: Check the EGR gasket under the valve. It is probably a leak. Torque the bolts to specs. Make sure the gasket is good though.

Question: I have a 96 Honda Civic bucks and it slips while trying to take off?

Answer: Check the transmission fluid, level and quality - there could be some transmission problems.

Question: I have a Dodge Caliber 2.0 CRD. It is running at about 150kph, and suddenly lost engine power with no boost. Could it be an EGR fault?

Answer: It seems like pressure built-in the tank (probably a suction control valve problem). Sometimes releasing the fuel cap can help.

Question: I have an old car that I have done a lot of work to, and on my way home after a stop light, I hit a higher rpm to shift up a hill. It hit about 3500 rpm, and it cut out, and had no throttle control. A few seconds later I had throttle control then it cut out again. Then like before it came back but it seemed like it didn't have as much power as it should. Could that be a bad EGR valve?

Answer: If your car has a throttle positon sensor, make sure the signal is increasing smoothly, if it skips it can have sometimes the same symptom. This might help:

https://hubpages.com/auto-repair/How-Do-You-Know-i...

Also, check the fuel system.

Question: I own a 2006 Volvo s40 1.6 Diesel manual. Seven months ago it lost throttle and presented delayed acceleration. The mechanics "found" (computer) the DPF, and pressure sensor was the problem. But two days after, the same issue came back. The EGR valve was changed, and the problem was solved for three months. Now they suspect it is the mass flow gas meter. In the meantime a gasket was changed in the injectors, to control oil leaks and it didn't work. Any help?

Answer: The problem could be in the fuel system, the fact that there was an oil leak may be a clue. Check and see if the oil didn't contaminate the injectors and take it from there.

Question: I have an '87 Nissan Hardbody D21 2WD standard shift. It's got the 2.4L Z24 TBI. My EGR system, I think, has caused head gasket damage. Could the EGR system damage the head gasket? I wanted to make sure it would be OK to delete the system. I'm also going to repair the head gasket now. What's your opinion of the difference between the Blue devil head gasket sealant or thermal gasket? I just bought the truck a few weeks ago.

Answer: A stuck-close or clogged EGR can increase engine temperature. If the problem leads to detonations, it can damage the engine. So it's possible. This problem is more common with EGR cooler failures when it causes loose of coolant. I personally wouldn't recommend deleting the system. It may lead to engine overheating, increase emissions, and driveability issues.

Aftermarket head gasket repair products can do the trick if the damage is not extensive. However, the repair might not be permanent. That said, I've known of people that have some success with Blue Devil and Steel Seal. You may want to do some research and see which will work best for the type of head gasket you are using in your particular application.

Question: I have a Passat B6 1.6 FSI. The check engine light is on. I checked it on the reader and it says there is an EGR problem, so I changed it with another one. I drove my car for 100 km, then the light went on again. I changed it again, and the same thing happened. What should I do?

Answer: Check the definitions for the trouble codes; also, a common problem with EGR valves are the passages. Once you remove the valve, you need to check/clean intake passages from carbon deposits that might be obstructing exhaust flow towards the chambers. If there's an obstruction problem, the CEL will keep coming on.

Question: I am driving a Mazda 2 DE. And when I disassembled the EGR, it's filled with water flowing out. My EGR is not water cooled. Thus, there shouldn't be water in there. Would this be a sign of leaking head gasket with coolant seeping into the cylinder area?

Answer: If there's coolant, you may have a cracked head, gasket or block. But there could be other symptoms as well if this is the case. If you found water, this most likely is the steam you see coming out the exhaust (from fuel burning) when starting the engine, usually in cold temperature climates.

Question: What other symptoms can cause an EGR valve to show that it's bad or, in other words, causing the engine light to stay on?

Answer: Possibly the EGR valve/intake passages are clogged, or there's a problem with the EGR system circuit. These other two posts may help:

https://axleaddict.com/auto-repair/How-to-Test-an-...

https://axleaddict.com/auto-repair/EGR-Valve-Clean...

Question: I have 99 Chevy 1500. It gave a P0404 code. The guy said EGR valve but the symptoms don't match. It is only hard to start. Turns over but takes 10 tries sometimes. Before only when it sat for more then 10hrs. now will do it even if it was started an hour before. Sometimes it starts after 1 or 2 but sometimes it will kill the battery trying. But once it starts it is perfect quiet as a mouse smooth. Doesn't cut off. Is that an EGR valve or why would it give p0404?

Answer: This is an electrically controlled valve. The problem could be in the circuit. But the valve can be sticking open, which is reported to the PCM. You may want to try first removing the valve and checking for carbon buildup. The valve can be checked with a scan tool and testing circuit voltages and grounds.

Question: Can the EGR valve be closed with a plate on a Duramax Diesel?

Answer: It can be done with a blocker plate, if you find a reliable shop to do it. It's possible that you'll need to clean the valve once in a while if oil from the PCV valve begins to accumulate.

Question: My car's def indicator turns on and off. What do I do?

Answer: There could be a problem with the pump. Check the codes.

Question: I have a Jaguar XF. The computer states I have a faulty EGR Valve. The only symptom I have is the car won't do more than 50mph (ca. 80 km/h) no matter how much I accelerate. Is it the ERG valve as the engine warning light comes on after about 30 minutes?

Answer: It's better to test the EGR valve and make sure there's where the problem is, even if the computer points to the valve. There could be another problem causing the computer to go into limp or safe mode to prevent more damage. You may need your vehicle repair manual to test the EGR valve.

Question: My 2010 Vauxhall Zafira was diagnosed with an EGR valve stuck on the P0400 code. I got it repaired from the dealer. Now it is having a problem with the gears. Are they related?

Answer: The EGR valve is part of the emission control system. A problem with the gears will be focused on the transmission.

Question: I have a 1997 Isuzu Rodeo. Sometimes it won't start. A light tap or two on the ERG valve would solve the problem. That doesn't work anymore. Could the erg valve be bad? I've tried taking it off and cleaning it.

Answer: There could be a leak in the system. You might want to check the valve and the gasket. This post may help:

https://hubpages.com/auto-repair/How-to-Test-an-EG...

Question: Why is there a recirculation of exhaust gases in a car?

Answer: It reduces the amount of harmful emission -- oxides of nitrogen (NOx). When you mix exhaust gases with the air-fuel mixture, the temperature drops a little bit. This also helps avoid pinging or knocking.

Question: I have a '08 Chrysler Aspen with HEMI. I changed my original EGR a year ago and now the code is back. Is this just a bad aftermarket EGR? I was told to always buy electronic EGR from a dealer. Is this likely the problem?

Answer: This can be the issue. Some models just won't take an aftermarket replacement, specially on electronic components. But, for peace of mind, you may want to run a diagnostic to make sure the same component is the one causing trouble again.