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EGR Modulator
- Remove vacuum hoses from modulator. Plug modulator ports No. 2 and No. 3. See Fig 1
. Connect hand-held vacuum pump to port No. 4 and apply vacuum. Vacuum should not hold. If vacuum holds, check for plugged modulator filter. If filter is not plugged, replace EGR modulator.
- Connect vacuum hose to modulator port No. 5. Blow into hose. Again apply vacuum to port No. 4. Vacuum should now hold. If vacuum does not hold, replace EGR modulator.
Courtesy of GENERAL MOTORS CORP.