Note On Intermittents

With engine at idle, manipulate EGR solenoid connector and PCM connector, and related wiring. EGR solenoid should remain energized (circuit No. 435 grounded) to block vacuum to EGR valve/vent vacuum to atmosphere. Listen for change in idle quality.

Drive vehicle with TP sensor at 8-15 degrees and engine speed at 1450-1650 RPM and try to duplicate code. With engine at idle, apply and release vacuum to EGR valve to check if EGR valve is binding. Turn engine off. Remove EGR valve and check for excessive carbon build-up restricting EGR flow or holding EGR valve open. Check for plugged, leaky, misrouted or nicked vacuum hoses.

Fig 1: Code P048 Schematic, EGR System Malfunction

Courtesy of GENERAL MOTORS CORP.

Fig 2: Code P048 Diagnostic Flow Chart - 1 Of 2, EGR System Malfunction

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Fig 3: Code P048 Diagnostic Flow Chart - 2 Of 2, EGR System Malfunction

Courtesy of GENERAL MOTORS CORP.