There are several fault codes available on the OBD computers that can indicate what and where a problem is with the EGR system. As mentioned above, the most common problem is clogged EGR ports in the intake, but cracked hoses and connectors can be other low cost (but common) causes for EGR problems. The recirculation of exhaust into the intake affects the combustion temperature and can result in excess pinging if not present as expected by the PCM.
