Welcome to Matthew's Volvo Site.
Have you erased the code? I am a firm believer in erasing codes and running the car to see if they return. Quite often the code is set by a one off occurence and nothing is actually wrong.
The EGR valve on the 960 is electronic and there are differing views on whether or not it can be cleaned.
I don't have a diagram for cleaning but to replace the EGR valve you need to remove the starter motor and oil dipstick pipe. Slacken the pipe connections to the EGR valve, slacken the EGR valve screws and remove the valve and seal.
Have you tested the EGR valve using the On-Board Diagnostic unit?
Work was good - retirement is better.
1996 850GLT 2.5 20v Estate Manual.
1995 Peugeot Boxer 2.5Tdi Autosleeper.
1984 244DL, Manual, Beige.
1987 744GLE, Manual, Green.
1991 960 3.0 24v, Auto, Silver.
1994 940T Wentworth, Auto, Blue.