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Diagnosis & Repair (Using OBD-II Scan Tool)

  1. Check all EGR system vacuum hoses. Replace vacuum hoses as necessary. Access ECM behind bottom center of instrument panel, in front of console. Ensure ignition is off. Disconnect ECM E8 connector. Turn ignition on. Connect a jumper wire between ground and terminal No. 23 (Black/White wire) at ECM E8 connector.
  2. With jumper wire connected, Vacuum Switching Valve (VSV) is on. Apply air pressure to VSV port "E". Air from port "E" should flow from port "F". See Figure. Disconnect jumper wire. Air from port "E" should flow from small filter on end of valve. If valve operates as specified, go to step 6). If valve does not operate as specified, go to next step.
  3. Turn ignition off. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 37-44 ohms at 68°F (20°C). Check for continuity between each terminal and body of valve. If continuity exists, replace VSV. If continuity does not exist, go to next step.
  4. Check VSV operation. Apply battery voltage to valve terminals. Apply air pressure to VSV port "E". Air from port "E" should flow from port "F". See Figure. Remove battery voltage from valve terminals. Air from port "E" should flow from small filter on end of valve. Replace VSV as necessary.
  5. Check for open or short circuit in wiring harness between instrument panel fuse block and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair wiring as necessary.
  6. Check EGR vacuum modulator. See SYSTEM/COMPONENT TESTS - 1.8L article. Replace as necessary. If EGR vacuum modulator is okay, check EGR valve. See SYSTEM/COMPONENT TESTS - 1.8L article. Replace as necessary. If EGR valve is okay, go to next step.
  7. Check Manifold Absolute Pressure (MAP) sensor. See SYSTEM/COMPONENT TESTS - 1.8L article. Replace MAP sensor as necessary. If MAP sensor is okay, replace ECM and retest.
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