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Home >> Toyota >> 1996 >> 4Runner Base, 4WD, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Tests W/Codes - 2.7L >> Circuit Tests >> DTC P0401 - Insufficient Exhaust Gas RECIRCULATION (EGR) Flow Detected >> Diagnosis & Repair (Using Toyota Scan Tester)
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Diagnosis & Repair (Using Toyota Scan Tester)

  1. Connect scan tester. See Figure. Turn ignition on. Read EGR gas temperature. If temperature is 50°F (10°C) or more, go to step 6). If temperature is 37.6°F (3.1°C), there is an open EGR temperature sensor circuit. If temperature is less than 50°F (10°C), go to next step.
  2. Disconnect EGR temperature sensor connector. Sensor is mounted in intake plenum. Connect a jumper wire between sensor wiring harness connector terminals.
  3. If EGR temperature displayed is not 318.7°F (159.3°C), go to next step. If temperature displayed is 318.7°F (159.3°C), inspect sensor connectors and terminals. Repair as necessary. If connectors are okay, replace sensor and retest.
  4. Remove jumper wire. Turn ignition off. Access ECM behind glove box. On A/T models, connect jumper wire between terminals No. 9 (Brown/Black wire) and No. 14 (Pink wire) at ECM E7 connector. See Figure. On M/T models, connect a jumper wire between terminals No. 9 (Brown/Black wire) and No. 3 (Pink wire) at ECM E7 connector. On all models, turn ignition on.
  5. If EGR temperature displayed is 318.7°F (159.3°C), inspect and repair open in circuits between ECM and EGR temperature sensor. If temperature displayed is not 318.7°F (159.3°C), replace ECM and retest.
  6. Inspect vacuum hoses. See appropriate illustration in M - VACUUM DIAGRAMS article. Repair as necessary. If all hoses are okay, inspect VSV. On scan tester, select ACTIVE TEST mode. Check operation of VSV when activated by scan tester. VSV is located near intake plenum.
  7. Start and run engine. With EGR system off, air from port "E" should exhaust from port "F". See Fig 1. With EGR system on, air from port "E" should not exhaust from port "F". If valve operates correctly, go to step 11). If valve does not operate correctly, go to next step.
  8. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 33-39 ohms at 68°F (20°C). Measure resistance between each terminal and body of valve. Resistance should be infinite. If resistance is not as specified, replace VSV. If resistance is as specified, go to next step.
  9. Check VSV operation. Apply battery voltage to VSV terminals. Air from port "E" should exhaust from port "F". See Fig 1. Remove battery voltage from valve terminals. Air from port "E" should not exhaust from port "F". Replace VSV as necessary.
  10. If VSV operates as specified in steps 8) and 9), inspect circuits between EGR VSV and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
  11. Inspect EGR vacuum modulator. See SYSTEM/COMPONENT TESTS article. Replace as necessary. If modulator is okay, inspect EGR valve. See SYSTEM/COMPONENT TESTS article. Replace as necessary. If components are okay, go to next step.
  12. Ensure all components are connected. Inspect EGR temperature sensor. Start and run engine. Using scan tester, select ACTIVE TEST mode (EGR system ON). Run engine at 4000 RPM for 3 minutes. Monitor EGR gas temperature. If temperature is 284°F (140°C) or more, replace ECM and retest. If temperature is less than 284°F (140°C), replace sensor.
Fig 1: EGR Vacuum Switching Valve ID (EVAP VSV Is Similar)
G96B10182Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
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