Vacuum Test
WARNING: This page is about a different car, the 1990 Cadillac Fleetwood and 1990 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
Connect a vacuum gauge to source side of EGR solenoid. Start engine and check that manifold vacuum is present. If not, repair vacuum circuit between EGR solenoid and throttle body.
Connect vacuum gauge to the EGR valve vacuum supply. No vacuum should be present when engine is at idle. If vacuum is present, go to CODE E48: EGR SYSTEM FAULT (2 OF 2).
With vacuum gauge hooked to EGR valve vacuum supply, disconnect the EGR valve solenoid connector. There should be 8 in. Hg at gauge. If not, repair leak or obstruction in EGR valve vacuum hose.