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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 at normal operating temperature and engine idling, push up on underside of EGR valve diaphragm. Engine RPM should drop.
  2. If engine RPM does not drop, clean EGR valve or passages. If RPM still does not drop, replace EGR valve. If engine RPM does drop, check for EGR valve diaphragm movement with idle speed change from 2000 RPM to idle. EGR valve diaphragm should not change.
  3. If EGR valve diaphragm moves with idle change, check Park/Neutral switch for open circuit or misadjustment of switch. If EGR valve diaphragm does not move, disconnect EST connector and ground test terminal. If EGR valve diaphragm moves, EGR valve is functioning properly.
  4. If EGR valve diaphragm still does not move, stop engine and disconnect EGR solenoid connector. Connect 12-volt test light between EGR solenoid connector terminals. Turn ignition on and ground test terminal. Test light should flash repeatedly.
  5. If test light flashes, check for vacuum to EGR solenoid at 2000-3000 RPM. If engine does not use a vacuum regulator, there should be at least 7 in. Hg vacuum at solenoid. If engine is equipped with a vacuum regulator, there should be 2-10 in. Hg vacuum.
  6. If vacuum is greater than 10 in. Hg, replace regulator. If vacuum is less than 2 in. Hg, vacuum at solenoid is okay and check EGR solenoid connections and/or faulty EGR solenoid.
  7. If test light was on steady, check for ground in wire to ECM terminal "T". If terminal is not grounded, check for faulty ECM. If test light is off, connect test light from each EGR connector terminal to ground and note light.
  8. If test light is on at both terminals, check for short to battery positive in wire to ECM terminal "T". Repair and recheck as required, ECM may be damaged.
  9. If test light is off, repair open in wire from solenoid to ignition. Check for blown fuse. If test light is on only at one terminal, check for open in wire to ECM terminal "T". If wire is not open, check resistance of EGR solenoid.
  10. Resistance should be over 20 ohms. If resistance is below 20 ohms, replace EGR solenoid and ECM. If resistance is over 20 ohms, ECM or connections may be faulty. If further testing is required, see appropriate diagnostic chart in COMPUTER COMMAND CONTROL article.
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