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Home >> Lexus >> 1997 >> 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 Tool)

Diagnosis & Repair (Using Lexus Scan Tool)

  1. Connect Lexus scan tool to DLC No. 3. Turn ignition on. Read EGR gas temperature. Temperature should be 50-302°F (10-150°C) (not immediately after driving). If temperature is as specified, go to step 5). If temperature is not as specified, go to next step.
    NOTE: If EGR gas temperature displayed is 37.6°F (3.1°C), there is an open in EGR temperature sensor circuit. If temperature displayed is 318.7°F (159.3°C), there is a short in EGR temperature sensor circuit.
  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, check sensor connectors and terminals. Repair as necessary. If connectors are okay, replace sensor and retest system.
  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 E8 connector and No. 22 (Brown wire) at ECM E9 connector. See Figure. Turn ignition on. EGR gas temperature displayed should be 318.7°F (159.3°C).
  4. If temperature displayed is not as specified, replace ECM and retest system. If temperature displayed is as specified, repair circuit(s) between ECM and EGR temperature sensor.
  5. Check vacuum hoses. Repair as necessary. If all hoses are okay, check VSV. Using scan tool, select ACTIVE TEST mode. Check operation of VSV when activated by scan tool. VSV is located near air intake chamber assembly.
  6. Start and run engine. With EGR system off, air should flow from port "G". See Fig 1. 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.
  7. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 27-33 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. Apply air pressure to port "E". Air should flow from port "G". Using jumper wires, apply battery voltage to VSV terminals. Again, apply air pressure to port "E". Air should flow from port "F". Replace VSV as necessary.
  9. If valve meets all specifications in steps 7) and 8), check wiring harness between EGR VSV and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
  10. Disconnect vacuum hose from EGR valve. Start engine. Apply vacuum to EGR valve. If engine runs rough or stalls, go to next step. If engine does not stall or run rough, replace EGR valve and retest system.
  11. Check EGR Vacuum Control Valve (VCV). See SYSTEM/COMPONENT TESTS article. Replace VCV as necessary. If VCV is okay, replace ECM and retest system.
Fig 1: Identifying Vapor Pressure Sensor VSV Vacuum Ports & EGR VSV Vacuum Ports
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