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Home >> Toyota >> 1998 >> Celica 2D Convertible, 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 OBD-II Scan Tool)
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Diagnosis & Repair (Using OBD-II Scan Tool)

  1. Check all EGR system vacuum hoses. Replace as necessary. Access ECM below passenger's side of instrument panel, underneath carpet near center console. Ensure ignition is off. Disconnect ECM E5 connector. Turn ignition on. Connect a jumper wire between ground and terminal No. 23 (Blue/Black wire) at ECM E5 connector.
  2. With jumper wire connected, Vacuum Switching Valve (VSV) is on. Air from port "E" should flow from port "G". 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 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 valve terminals. Air from port "E" should flow from port "G". 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 left fuse block in engine compartment 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.
  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.
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