The exhaust gas recirculation (EGR) valve is used to divert a small amount of exhaust gases back to the motor. The gases reduce the combustion temperature to reduce emissions. Bad EGR valves cause an increase in emissions as well as other problems.
The EGR valve can be removed and inspected for damage. Cracks, corrosion or other damage noted to the body or internal components will require the valve to be replaced. Defective diaphragms are a common cause of EGR valve failure, but the diaphragm cannot be seen on most valves.
Deposits at the bottom of the EGR valve can cause the valve to fail. The deposits can be cleaned, but care must be used to not damage the diaphragm inside the valve. Also, the small tube or passageway that the exhaust gases pass through back to the engine can become clogged with deposits. A small wire or similar object can be used to probe the tube for obstructions.
Diagnostic scanners can be used to determine if the EGR valve is working. Auto repair shops can complete the testing, or scanners can be purchased from auto parts stores. Equipment is available to test EGR valve performance, but the equipment is much more expensive than buying a new valve.