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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 OBD-II Scan Tool)

Diagnosis & Repair (Using OBD-II Scan Tool)

  1. Disconnect EGR temperature sensor. Connector is located near throttle body. Using ohmmeter, measure resistance between sensor terminals. If resistance is 2500-600,000 ohms (not immediately after driving), go to next step. If resistance is not 2500-600,000 ohms, replace EGR temperature sensor.
  2. Check for an open or short in wiring harness between EGR temperature sensor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, go to next step.
  3. Check all EGR system vacuum hoses. Replace hoses as necessary and retest system. If vacuum hoses are okay, access ECM behind glove box. Ensure ignition is off. Disconnect ECM E8 harness connector. Turn ignition on. Connect a jumper wire between ground and terminal No. 12 (Yellow/Green wire) at ECM E8 connector.
  4. Apply air pressure to VSV port "E". See Figure. With jumper wire connected to ground, air should flow from port "F". With jumper wire disconnected, air should flow from port "G". If VSV operates as specified, go to next step. If VSV does not operate as specified, replace VSV and retest system.
  5. Check for an open in wiring harness between EGR VSV and ECM. Repair as necessary and retest system. If wiring is okay, check EGR valve. See SYSTEM/COMPONENT TESTS article. Replace EGR valve as necessary and recheck system. If EGR valve is okay, go to next step.
  6. Check EGR Vacuum Control Valve (VCV). See SYSTEM/COMPONENT TESTS article. Replace VCV as necessary. If VCV is okay, replace ECM and retest system.
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