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Pulse-Width Modulated EGR Valve

  1. Check vacuum lines for leaks and electrical connectors for proper installation. Place transmission in Park or Neutral. With engine idling at normal operating temperature, push up on underside of EGR valve diaphragm. Engine RPM should drop. If engine RPM does not drop, clean EGR valve and passages.
  2. Check for EGR valve diaphragm movement with engine RPM change from 2000 RPM to idle. EGR valve diaphragm should not change. If EGR valve diaphragm moves with RPM change, check Park/Neutral switch for open circuit or misadjustment. If EGR valve diaphragm does not move, disconnect ALDL test connector and ground test terminal. If EGR valve diaphragm moves, EGR valve is functioning properly.
  3. If EGR valve diaphragm still does not move, stop engine and disconnect EGR solenoid connector. Connect 12-volt test light to EGR solenoid connector terminals. Turn ignition on and ground ALDL test terminal. Test light should flash repeatedly.
  4. If test light remains on steadily, check for short to ground in wire to ECM. If wire is okay, ECM is faulty. If test light flashes, go to step 5). If light is off, connect test light from each EGR connector terminal to ground. If light is off, repair open in wire from solenoid to ignition (including fuse). If light is on at both terminals, check for a short to voltage in wire to ECM terminal.
    NOTE: ECM may have been damaged from a short to voltage.
  5. Repair and recheck. If light was on for one terminal, check for an open in wire to ECM. If wire is okay, check resistance of EGR solenoid. If EGR solenoid resistance is not over 20 Ohms, replace EGR solenoid and ECM. If resistance is over 20 Ohms, check for faulty ECM connection or ECM.
  6. Check for vacuum at EGR solenoid at 2000-3000 RPM. If engine does not use a vacuum regulator, there should be at least 7 in. Hg at solenoid. If engine is equipped with a vacuum regulator, there should be 2-10 in. Hg.
  7. If vacuum is greater than 10 in. Hg, replace regulator. If vacuum is less than 2 in Hg, vacuum at solenoid is okay. Check EGR solenoid connections and/or faulty EGR solenoid. To test EGR solenoid for all models except Cadillac, see appropriate EGR SYSTEM article in the ENGINE PERFORMANCE section. To test EGR solenoid for Cadillac models, see PERFORMANCE CHART 7 in DFI TESTS W/CODES article in the ENGINE PERFORMANCE section.
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