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Home >> Toyota >> 1997 >> Avalon XL >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Tests W/Codes >> Circuit 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. Sensor is located on manifold between EGR valve and intake manifold. Using ohmmeter, measure resistance between sensor terminals (not immediately after driving vehicle). If resistance is 2500-600,000 ohms, go to next step. If resistance is not 2500-600,000 ohms, replace sensor and retest.
  2. Check for open or short circuit in wiring harness between EGR temperature sensor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair wiring as necessary and retest. If wiring harness is okay, go to next step.
  3. Check all EGR system vacuum hoses. Replace hoses as necessary. If vacuum hoses are okay, access ECM behind glove box. Ensure ignition is off. Disconnect ECM E6 connector. Turn ignition on. Connect a jumper wire between ground and terminal No. 12 (Black/White wire) at ECM E6 connector.
  4. Apply air pressure to EGR Vacuum Switching Valve (VSV) port "E". VSV is located under "V" bank cover on top of engine. With jumper wire connected, air should flow from port "G". See Figure. With jumper wire disconnected, air should flow from port "F". If VSV operates as specified, go to step 7). If VSV does not operate as specified, go to next step.
  5. Remove EGR VSV. Using ohmmeter, measure resistance between VSV terminals. Resistance should be 27-33 ohms at 68°F (20°C). Measure resistance between each terminal and body of VSV. Resistance should be infinite. If resistance is not as specified, replace VSV. If resistance is as specified, go to next step.
  6. Check VSV operation. Apply battery voltage to VSV terminals. Apply air to VSV port "E". Air should flow from port "F". Remove battery voltage from VSV terminals. Air should flow from port "G". Replace VSV as necessary and retest. If VSV meets all specifications in steps 5) and 6), check for open in EGR VSV circuits between fuse block and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
  7. Disconnect vacuum hose from EGR valve. Connect a vacuum pump to EGR valve. Start engine. Apply vacuum to EGR valve. If engine does not run rough or stall, replace EGR valve and retest. If engine runs rough or stalls, check EGR Vacuum Control Valve (VCV). See SYSTEM/COMPONENT TESTS article. Replace as necessary. If VCV is okay, replace ECM and retest.
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