Help With Those Troublesome EGR Valve Codes!
Today I'd like to throw some thoughts out on how to check a car's EGR Valve and related EGR system components for proper operation. Most basic automotive systems can be pinpoint tested down to a faulty component in a matter of less than 20 minutes, regardless of the code. You will need a scan tool, preferably capable of monitoring the car's sensor values (sometimes referred to as PID's), a vacuum pump and a pressure gauge. A scan tool is not completely necessary, and I will give you a work around in the testing procedures. That's about it! All systems are quite similar in design but some car manufacturers may use different names for some of their components. For simplicity's sake we'll base our diagnosis on a typical Ford EGR system. Let's get started!
So what is an EGR system and how does it work? EGR stands for Exhaust Gas Recirculation, and as its name implies, this system allows exhaust gasses from your car to be re-circulated into the engine, helping to reduce emissions. These systems are mostly comprised of the EGR valve, a DPFE (Delta Pressure Feedback EGR) sensor, hoses, a vacuum regulator, some vacuum lines, wiring, the computer and the exhaust tube leading to the valve itself. The car's wiring can be tested in the normal fashion (see our article on Automotive Circuit Testing here), and all vacuum lines can be checked easily for cracks, leaks and correct routing. We will be discussing the easiest way to test the 3 remaining components: the EGR valve, EGR vacuum regulator and DPFE sensor (or similar flow sensor). So if you have a scan tool hook it up and let's go, if not read on and we'll get around that too!
Next, start the vehicle and check DPFE voltage reading at idle. If it is out of spec., first make sure that the 2 hoses going to the sensor are not ripped, kinked, restricted or disconnected. These hoses go to the EGR tube and there is an orifice in that tube between the locations where the hoses branch out. The sensor uses the difference in pressure between these two hoses to determine exhaust flow through the tube (thus the term Delta Pressure Feedback EGR). If these are all in order then next verify that there is no EGR flow by disconnecting the vacuum line going to the car's EGR valve. This isolates the control side of the EGR system and is the easiest way to be certain the valve is not being commanded open. There is still the possibility that the valve may be sticking open slightly, or be carboned up causing it to leak by, but this would typically also give you a driveability concern such as a rough idle. If you suspect the valve to be hanging open I would suggest removing it and bench testing it for leakage past the pintle (the needle that restricts flow when no vacuum is applied). I should mention that EGR valves rarely go bad. I have seen many cars come in for diagnosis with EGR system codes and a new EGR valve already installed! Don't make this mistake!
Okay, back to the tests! So with the vacuum line disconnected (and the engine still running), recheck your reading on the DPFE sensor. If it is now in spec, then your problem is on the control side. In other words the EGR is being opened when it shouldn't be. You now know the DPFE, EGR valve and tube and hoses are okay and we can move on to test the EVR (EGR Vacuum Regulator), part of the system. If the reading did not change, then you could suspect a leaking EGR valve, allowing uncommanded flow of exhaust gases. I would remove and bench test the valve for leakage.
A couple other things to check with this system are excessive back pressure or a restricted EGR tube. These are quick and easy to check for. First remove the hose from the DPFE sensor that is farthest from the engine. You should be able to feel slight exhaust flow through the hoses (careful exhaust gases are hot - use reasonable care). Use a pressure guage and check that there is no more than 4 psi in the line with the engine running. If the reading is higher suspect a restricted exhaust system to be causing excessive pressure. If there is no flow, then suspect a restricted EGR tube below the hose connections. I have also seen once, that the orifice in the tube seperated so there was no pressure difference in the hoses when the EGR system was flowing. I have only seen this once but if it happens to you it could throw you for a loop, especially if you didn't understand how the system actually worked!
The engine side of the system can also become plugged with carbon deposits preventing flow of gases. A quick way to check for this is to apply vacuum to the EGR valve and monitor engine operation. Assuming the EGR valve is ok the engine should begin to stumble and possibly even stall as vacuum is applied to the valve and the pintle opens. Your DPFE voltage should also approach 4.5 volts. If you notice no engine performance change then you are not flowing EGR gases. Turn the engine off and apply full vacuum to the EGR valve, and then release quickly. If the valve is working you should notice a thump type noise as it closes. Do this a couple of times to verify the valve is operating properly. If it seems to be, you could then remove and bench test it. If all is well here then you have a restriction in the manifold ports or other engine side area.
So, backing up...If you had previously disconnected the vacuum line from the valve and readings from the DPFE were now correct it is a concern on the control side. Check the vacuum lines from the EGR vacuum regulator (follow the vacuum line back from the valve to find it) to the valve, and also make sure there is supply vacuum on the other port of the regulator. The regulator is normally closed and when the computer wants EGR flow, it turns the vacuum regulator on and vacuum is sent to open the EGR valve, allowing flow of exhaust up the tube and into the engine. So if the lines are good and we have vacuum at the regulator with the engine running then the only component left to test is the EVR. There are a few ways of doing this. If you have a scan tool capable of controlling actuators or pids you can command the EVR on and check for vacuum at the EGR valve as the regulator opens. If you do not notice vacuum at the EGR valve as the EVR is commanded on and you do have supply vacuum at the EVR connector then check the EVR, wiring and computer control. Also check to be sure the vent is not plugged, there is often a cap that can be pulled off which allows you to check the vent and its foam filter. Another way you can check the EVR on many vehicles (not all) if you don't have a scan tool capable of PID manipulation is to do the following: Run a Key On Engine Running (KOER) self test, and have your vacuum gauge hooked to the vacuum line coming in to the EGR valve. Watch the gauge closely while the test runs. The gauge should climb up to 5-10 in.hg once or twice during the KOER test. This is because the computer commands the EVR on so the EGR valve will open and then the computer looks for a voltage change on the DPFE sensor. This is how the computer checks operation of this sensor. If the gauge doesn't move during the KOER test then you need to check the EVR, related wiring and possibly (not very likely) a computer concern. This will likely set a memory code for insufficient EGR flow so be sure to clear codes after your testing is completed.
Now remember these procedures are based around a typical OBD II Ford system but the overall principals should hold on most vehicle lines. So now you know how everything works, here's the quick test I perform (about 10 minutes tops!), on all vehicles with EGR system concerns:
Engine running, so be careful and use proper care! Find the EGR valve and disconnect the vacuum line going to the top of the valve. There should be no vacuum there at this time. If there is then check for proper EVR (EGR vacuum regulator) operation and vacuum line routing. Repair and continue testing. Hook up your hand vacuum pump to the EGR valve and slowly apply a vacuum. If the EGR valve is functioning then the engine should begin to run poorly and stumble. If you apply full vacuum and notice no RPM change or can't pull a vacuum at all, then check for a faulty diaphragm in the valve or a restriction of the EGR tube, exhaust or intake manifold EGR ports. I have run across many concerns where the EGR passages in the intake manifolds become plugged with carbon and prevent EGR flow, so try to keep this in mind during testing. Repair and continue testing. Monitor your DPFE reading as you apply vacuum to the EGR valve the reading should began to climb to between 4-5 volts under full vacuum and the engine may stall. If the engine does stumble, but your reading does not change then check DPFE hoses and EGR tube for restrictions or leakage and component test DPFE and related circuits.
And that's that! You've tested the entire EGR system, regardless of codes in a very short time frame. Always remember to clear any codes you may have set during testing. EGR valves are replaced way too frequently due to lack of training and system knowledge. The EGR valve itself is one of the least likely parts to fail in the system, and if my diagnosis led me there I would component test the valve on the bench before replacing it ! I hope you found this article interesting. Seen any really unusual EGR system concerns? Drop us a line and share your experience! Enjoy the day!
The engine-light-help.com Team