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Home >> Lexus >> 1996 >> SC 300 Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Tests >> DTC P0401 - Insufficient Exhaust Gas RECIRCULATION (EGR) Flow Detected >> Diagnosis & Repair (Using Lexus Scan Tester)

Diagnosis & Repair (Using Lexus Scan Tester)

  1. Remove instrument panel fuse cover. Connect Lexus scan tester. Turn ignition on. Read EGR gas temperature. Temperature should be 50°F (10°C). If temperature is as specified, go to step 5). If temperature is not as specified, go to next step. If temperature displayed is 37.6°F (3.1°C), there is an open EGR gas temperature sensor circuit. Repair as necessary.
  2. Disconnect EGR gas temperature sensor harness connector. Connector is located underneath throttle body. Connect jumper wire between harness connector terminals. EGR gas temperature displayed should be 318.7°F (159.3°C). If temperature displayed is not as specified, go to next step. If temperature displayed is as specified, inspect sensor connectors and terminals. Repair as necessary. If connectors are okay, replace sensor and retest.
  3. Remove jumper wire. Turn ignition off. Access ECM behind glove box. Connect Check Harness "A" (SST 09990-01000) to ECM. See TEST PREPARATION under SELF-DIAGNOSTIC SYSTEM. Connect jumper wire between ECM harness connector terminals No. 46 (Black/Red wire) and No. 65 (Brown wire) at ECM "B" connector. See Figure. Turn ignition on. EGR gas temperature displayed should be 318.7°F (159.3°C).
  4. If temperature displayed is as specified, locate and repair open in circuits between ECM and EGR gas temperature sensor. If temperature displayed is not as specified, replace ECM and retest.
  5. Inspect vacuum hoses. 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.
  6. Start and run engine. With EGR system off, no air should flow from port "F". See Figure. With EGR system on, air should flow from port "F". If valve operates correctly, go to step 10). If valve does not operate correctly, go to next step.
    Fig 1: Identifying EGR VSV Vacuum Ports (EVAP VSV Is Similar)
    G96D09634Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  7. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 39-45 ohms. Measure resistance between each terminal and body of valve. Resistance should be infinite. If resistance is as specified, go to next step. If resistance is not as specified, replace VSV.
  8. Using jumper wires, apply battery voltage to VSV terminals. Air should flow from port "F". Remove jumper wires from VSV terminals. No air should pass through port "F". Replace VSV as necessary.
  9. If valve meets all specifications in steps 7 and 8), inspect circuits between EGR VSV and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
  10. Inspect EGR vacuum modulator. See EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING article. Replace as necessary. If modulator is okay, inspect EGR valve. See SYSTEM & COMPONENT TESTING article. Replace as necessary. If EGR valve is okay, go to next step.
  11. Ensure all components are connected. Inspect EGR gas temperature sensor. Start and run engine. Select ACTIVE TEST mode on scan tester (EGR system ON). Run engine at 4000 RPM for 3 minutes. Monitor EGR gas temperature. Temperature should be 284°F (140°C) or more.
  12. If temperature is not as specified, replace sensor. If temperature is as specified, replace ECM and retest.
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