Vacuum Test

Connect vacuum gauge to source side of EGR solenoid. Start engine. Manifold vacuum should be present. If vacuum is not present, repair leaks or obstruction between EGR solenoid and throttle body.
Connect vacuum gauge to EGR valve vacuum supply hose. Vacuum should not exist with engine at idle. If vacuum is present, go to PCM CODE E048 (2 OF 2) .
With gauge attached to EGR valve vacuum supply hose, disconnect EGR solenoid connector. With engine at idle, vacuum reading should be greater than 8 in. Hg. If vacuum is not greater than 8 in. Hg, repair leak or obstruction in EGR valve vacuum hose.

Fig 1: PCM Code E048, Schematic, EGR System Fault

Courtesy of GENERAL MOTORS CORP.

Fig 2: PCM Code E048, Flow Chart, EGR System Fault (1 Of 2)

Courtesy of GENERAL MOTORS CORP.

Fig 3: PCM Code E048 1 Of 2