Pcm Code P048 - EGR System Fault: Notes
WARNING: This page is about a different car, the 1993 Cadillac Seville and 1993 Cadillac Eldorado. However, it is still accessible from the selected car via links, so may be relevant.
To perform test, PCM turns off EGR flow to engine and monitors oxygen sensor (closed loop) integrator. With EGR off, integrator should swing to a greater value, reflecting leaner air/fuel mixtures. If integrator does not swing to a greater value, PCM assumes either EGR was turned off before test started or EGR is flowing and PCM does not have ability to turn it off. PCM monitors EGR 5 times in a given key cycle. If EGR does not respond 3 or more times during a key cycle, PCM Code P048 is set.