Almost every manufacturer has issued Technical Service Bulletins (TSB) relating to EGR issues. Always check for TSBs, especially if your customer appears to be having an issue with the part. EGR related TSBs may involve a software calibration update for the PCM, a manufacturer’s recall, a redesigned intake manifold or EGR valve, an updated sensor or solenoid, or an improved cleaning procedure.
If regular maintenance, such as oil changes and tune ups including PCV valve replacement and fuel injection service, are not performed, then accelerated sludge build up in the engine will eventually clog the EGR passages.
A restricted catalytic converter or exhaust system will increase back-pressure, causing excessive EGR flow. The vehicle will lack power and may set EGR flow-related trouble codes.
Performance exhaust systems or an “empty” catalytic converter will reduce back-pressure and also set EGR flow trouble codes.
Regular Tune Ups and Oil Changes Reduces Sludge Build Up
A "Flash" Update of the PCM Calibration May Be Necessary to Correct Some Emissions Issues
PCM Flash Programming
Emissions system failures may not always be due to an actual hard part failure. Often, the emissions control strategy programmed into the PCM may need to be “adjusted." This requires updating the PCM calibration software by flash programming. This is similar to updating the software in your home computer to fix a security loophole in your web browser for example.