In California on Gasoline Cars part of the Emissions check is visual. The Tech has to say yes or no to items that are supposed to be on the Car and enters them in the Computer.

So if they ever decided to pay attantion the Diesels there is going to be a visual check to see if an EGR is connected or not.
They also used to disconnect the EGR Vacuum Hose and hook up something like Mighty Vac to see if the EGR worked or not.

Also out here they test you Fuel Cap.

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84 300D, 82 Volvo 244Gl Diesel