Note On Intermittents

With engine at idle, manipulate EGR solenoid connector and related wiring. Listen for a change in idle quality. Drive vehicle with throttle angle at 8-15 degrees and engine at 1450-1650 RPM to try to duplicate code. Remove EGR valve, and check it for carbon build-up which would restrict EGR flow and for foreign materials holding EGR valve open. Check for pinched, cut, kinked, misrouted or blocked vacuum passages and/or vacuum hoses reducing EGR flow. Check for EGR valve binding in up or down position.

Fig 1: PCM Code P048 Schematic - EGR System Fault

Courtesy of GENERAL MOTORS CORP.

Fig 2: PCM Code P048 Flow Chart (1 Of 2) - EGR System Fault

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Fig 3: PCM Code P048 Flow Chart (2 Of 2) - EGR System Fault

Courtesy of GENERAL MOTORS CORP.