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Home >> Lexus >> 1996 >> ES 300 >> 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 temperature sensor circuit. Repair as necessary.
  2. Disconnect EGR 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 jumper wire between ECM harness connector terminals No. 14 (Gray/Yellow wire) at ECM E9 connector and No. 22 (Brown wire) at ECM E8 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 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. VSV is located under intake plenum cover.
  6. Start and run engine. With EGR system off, air should exhaust from small filter on end of valve. With EGR system on, air should pass through valve and exit vacuum fitting at bottom of valve. If valve operates correctly, go to step 10). If valve does not operate correctly, go to next step.
  7. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 26-46 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 exhaust from small filter on end of valve. Remove jumper wires from VSV terminals. Air should pass through valve. 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 TESTS article. Replace as necessary. If modulator is okay, inspect EGR valve. See SYSTEM/COMPONENT TESTS article. Replace as necessary. If EGR valve is okay, go to next step.
  11. Ensure all components are connected. Inspect EGR 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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