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Home >> Toyota >> 1998 >> Celica 2D Hatchback, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Tests W/Codes >> Self-Diagnostic Tests >> DTC P0401: Insufficient Exhaust Gas RECIRCULATION (EGR) Flow Detected >> Diagnosis & Repair (Using Toyota Scan Tool)
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Diagnosis & Repair (Using Toyota Scan Tool)

  1. Check all EGR system vacuum hoses. See appropriate illustration in VACUUM DIAGRAMS article. Repair vacuum hoses as necessary. If all hoses are okay, check VSV. Using scan tool, select ACTIVE TEST mode. Check operation of VSV when activated by scan tool. VSV is mounted on top left rear of engine.
  2. Start and run engine. With EGR system off, air from port "E" should flow from small filter on end of valve. See Fig 1. With EGR system on, air from port "E" should flow from port "G". If valve operates as specified, go to step 6). If valve does not operate as specified, go to next step.
  3. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 33-39 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 air pressure to VSV port "E". Apply battery voltage to VSV terminals. Air from port "E" should flow from port "G". See Fig 1. Remove battery voltage from valve terminals. Air from port "E" should flow from small filter on end of valve. Replace VSV as necessary. If VSV operates as specified, go to next step.
  5. Check for open or short circuit in wiring harness between left fuse block in engine compartment fuse block and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
  6. Perform EXHAUST GAS RECIRCULATION (EGR) SYSTEM TEST. See EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM/COMPONENT TESTS article. Repair as necessary. If no problem is indicated, check EGR vacuum modulator. See EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM/COMPONENT TESTS article. Replace EGR vacuum modulator as necessary. If EGR vacuum modulator is okay, go to next step. If components are okay, go to next step.
  7. Check Manifold Absolute Pressure (MAP) sensor. See appropriate SYSTEM/COMPONENT TESTS article. Replace MAP sensor as necessary. If MAP sensor is okay, replace ECM.
Fig 1: Identifying EGR VSV
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