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Home >> Toyota >> 1998 >> T100 DX, 4WD, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Tests W/Codes - V6 >> Self-Diagnostic Tests >> DTC P0401: Insufficient Exhaust Gas RECIRCULATION (EGR) Flow Detected (2WD 1/2 Ton Models With Regular Cab) >> Diagnosis & Repair (Using Toyota Scan Tool)
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Diagnosis & Repair (Using Toyota Scan Tool)

  1. Connect scan tool. See Figure. Turn ignition on. Using scan tool, read EGR gas temperature. If temperature is 50°F (10°C) or more, go to step 6). If temperature is less than 50°F (10°C), go to next step.
    NOTE: If EGR gas temperature is 37.6°F (3.1°C), an open exists in EGR temperature sensor circuit.
  2. Disconnect EGR temperature sensor connector. Sensor is mounted on EGR valve on top right rear of engine. Connect jumper wire between sensor wiring harness connector terminals.
  3. If EGR temperature displayed is not about 318°F (159°C), go to next step. If temperature displayed is about 318°F (159°C), check sensor connector and terminals. Repair as necessary. If connector is okay, replace EGR temperature sensor.
  4. Remove jumper wire. Turn ignition off. Access ECM behind passenger's side kick panel. Connect a jumper wire between terminal No. 14 (Pink wire) at ECM E5 connector and terminal No. 22 (Brown/Black wire) at ECM E6 connector. See Figure. Turn ignition on.
  5. If EGR temperature displayed is about 318°F (159°C), locate and repair open circuit in wiring harness between ECM and EGR temperature sensor. If temperature displayed is not about 318°F (159°C), replace ECM.
  6. Check vacuum hoses. See appropriate illustration in VACUUM DIAGRAMS article. Replace vacuum hoses as necessary. If all hoses are okay and routed properly, check EGR VSV. Using scan tool, select ACTIVE TEST mode. Check operation of EGR VSV when activated by scan tool. EGR VSV is located on top left rear of engine.
  7. Apply air pressure to EGR VSV port "E". See Fig 1. With EGR system off, air from port "E" should flow from small filter on end of EGR VSV. With EGR system on, air from port "E" should flow from port "G". If EGR VSV operates as specified, go to step 11). If EGR VSV does not operate as specified, 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 VSV terminal and body of EGR VSV. Resistance should be infinite. If resistance is not as specified, replace EGR VSV. If resistance is as specified, go to next step.
  9. Check EGR VSV operation. Apply battery voltage to EGR VSV terminals. Apply air pressure to EGR VSV port "E". See Fig 1. Air from port "E" should flow from small filter on end of EGR VSV. Remove battery voltage from valve terminals. Air from port "E" should flow from port "G". Replace EGR VSV as necessary. If EGR VSV operates as specified, go to next step.
  10. Check for open circuit in wiring harness between EGR VSV and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair wiring as necessary.
  11. Check EGR vacuum modulator. See appropriate SYSTEM/COMPONENT TESTS article. Replace EGR vacuum modulator as necessary. If EGR vacuum modulator is okay, check EGR valve. See appropriate SYSTEM/COMPONENT TESTS article. Replace EGR valve as necessary. If components are okay, go to next step.
  12. Ensure all components are connected. Check EGR temperature sensor. Start and run engine. Using scan tool, 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. If temperature is less than 284°F (140°C), replace EGR temperature sensor.
Fig 1: Identifying EGR Vacuum Switching Valve (VSV)
G95F31380Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
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