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Home >> Toyota >> 1999 >> Avalon XLS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics >> Diagnostic Tests >> DTC P0401: Insufficient Exhaust Gas RECIRCULATION (EGR) Flow Detected >> Diagnosis & Repair (Using OBD-II Scan Tool)
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Diagnosis & Repair (Using OBD-II Scan Tool)

  1. Disconnect EGR temperature sensor harness connector. EGR temperature sensor is located on manifold, between EGR valve and intake air chamber. Measure resistance between EGR temperature sensor terminals (component side). If resistance is 2.5-600 k/ohms, go to next step. If resistance is not 2.5-600 k/ohms, replace EGR temperature sensor.
  2. Check for open or short in wiring between EGR temperature sensor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. If problem exists, repair wiring as necessary. If problem does not exist, go to next step.
  3. Check plugged, cracked and disconnected EGR system vacuum hoses. See appropriate illustration in VACUUM DIAGRAMS article. If problem exists, repair vacuum hoses as necessary. If problem does not exist, go to next step.
  4. Access ECM behind glove box. Turn ignition off. Disconnect ECM harness connector E6. See Figure. Using a jumper wire, backprobe between ground and terminal No. 18 (Black/White wire) at ECM E6 connector. Apply air pressure to EGR Vacuum Switching Valve (VSV) port "E". EGR VSV is located under "V" bank cover on top of engine. With jumper wire connected, air should flow from port "F". See Figure. With jumper wire disconnected, air should flow from port "G". If EGR VSV operates as specified, go to step  7. If EGR VSV does not operate as specified, go to next step.
  5. Disconnect EGR VSV harness connector. Measure resistance between EGR VSV terminals (component side). Resistance should be 27-33 ohms at 68°F (20°C). Measure resistance between each terminal and body of EGR VSV (component side). Resistance should be infinite. If resistance is not as specified, replace EGR VSV. If resistance is as specified, go to next step.
  6. Apply battery voltage to EGR VSV terminals (component side). Apply air to EGR VSV port "E". Air should flow from port "F". Remove battery voltage from VSV terminals. Apply air to EGR VSV port "E". Air should flow from port "G". If EGR VSV does not operates as specified, replace EGR VSV. If EGR VSV operates as specified, check for open in EGR VSV circuits between fuse block in left side of engine compartment and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
  7. Disconnect vacuum hose from EGR valve. Start engine and let idle. Apply vacuum to EGR valve. If engine does not run rough or stall, replace EGR valve or clean EGR passage. If engine runs rough or stalls, go to next step.
    8. NOTE: EGR position sensor is an integral part of EGR valve.
  8. Check EGR position sensor and EGR VCV. See EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - V6 & V8 article. If problem exists, repair as necessary. If problem does not exists, replace ECM.
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