THE ABCs of EGR Part II

Testing
Armed with the basics on the different types of vacuum-controlled EGR systems, you are now ready to test the system. We recommend consulting a service manual for your specific vehicle, paying special attention to safety precautions.


Keep in mind that a lot of configurations exist. For instance, certain models have a vehicle speed sensor that is used in connection with vacuum delivery to the valve. Unless the vehicle is traveling above a certain speed (25 to 30 mph), vacuum will not be routed to the valve. You can imagine that testing such a system would require specific techniques and safety precautions. The manual will inform you of such information.

Rules of Repair
Here are a few basic rules of thumb for diagnosis and repair. All tests should be performed on a fully warm engine (although the "passage test" could be done before the engine is fully warm, as noted below). If the "Check Engine" malfunction indicator lamp is illuminated, a diagnosis should be performed to determine the cause. It is likely that a failure in the EGR system will cause the lamp to light up. If that is the case, proceed with the testing.


In addition, the exhaust and intake passages to the valve should be clear. An easy way to test this is to push up on the underside of the valve while the engine is idling. (Again, be aware of how hot the valve is to the touch! Let the engine cool down a bit, if needed, before proceeding with this test.) The engine should idle roughly, or stall if the passages are clear.


On the non-internally backpressure-controlled valves, it's possible to apply vacuum to the valve with a handheld vacuum pump. If the valve holds vacuum and lifts, and the engine idles roughly, you then know that the valve is good and the passages are clear.