There's a whole host of parts and potential failure mechanisms for EGR systems. I'd be curious to know what make and year your coworker was experienced with. I know we had some issues as recently as 2013, but our stuff has been pretty solid since then as far as I know. I'm a reliability engineer for PACCAR, parent company of Kenworth and Peterbilt. I focus more on trucks in development than current product, but I still hear about the big issues with our powertrain (not with the Cummins gear though).
Part of the reason emissions components get the brunt of the anguish is because we are forced to turn on a dash light when a malfunction is detected even if it has no effect on the drivability of the vehicle. If the offset on a NOx sensor is too high, dashlamp. If the SCR efficiency is too low, dashlamp. Even the ambient air temp sensor is part of the emissions equipment because it is used to control fueling, and a bad sensor can lead to excess soot or NOx production. Meanwhile, the driver doesn't notice any symptoms other than a dashlamp.
Yes it does increase costs. We have to answer not just to the operators but also to the regulatory agencies. Sometimes those two "customers" have competing requirements. If we don't meet most of the operators demands we sell fewer trucks. If we don't all of the agencies demands we sell 0 trucks because they won't certify our vehicles. And they are coming after gliders too. We tried to price them so high no one would buy them. Not sure how many we still sell, if any.
