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Home >> Lexus >> 1996 >> SC 300 Automatic >> 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 Tester)

Diagnosis & Repair (Using OBD-II Scan Tester)

  1. Disconnect EGR gas temperature sensor 2-pin connector. Connector is located at rear of intake plenum. Using ohmmeter, measure resistance between sensor terminals. If resistance is 600 k/ohms or less, go to next step. If resistance is more than 600 k/ohms, inspect sensor. See SYSTEM & COMPONENT TESTING article. Replace sensor as necessary.
  2. Turn ignition on. Using DVOM, measure voltage between sensor harness connector terminals. If voltage is 4.5-5.5 volts, go to step 4). If voltage is not 4.4-5.5 volts, go to next step.
  3. Access ECM behind glove box. Connect Check Harness "A" (SST 09990-01000) to ECM. See TEST PREPARATION under SELF-DIAGNOSTIC SYSTEM. Measure voltage between terminals No. 46 (Black/Red wire) and No. 65 (Brown wire) at ECM "B" connector. See Figure. If voltage is 4.5-5.5 volts, inspect circuits between EGR gas temperature sensor and ECM for open circuit. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If voltage is not 4.4-5.5 volts, replace ECM and retest.
  4. Inspect all EGR system vacuum hoses. Replace as necessary. If vacuum hoses are okay, access ECM behind glove box. Connect Check Harness "A" (SST 09990-01000) to ECM connectors, leaving ECM disconnected. See TEST PREPARATION under SELF-DIAGNOSTIC SYSTEM. Turn ignition on. Connect a jumper wire between ground and terminal No. 75 (Gray wire) at ECM "B" connector.
  5. Vacuum Switching Valve (VSV) is located under intake plenum. With jumper wire connected, VSV is on. Air should flow from port "F". See Figure. Disconnect jumper wire. No air should flow from port "F". If valve operates correctly, go to step 9). If valve does not operate correctly, go to next step.
  6. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 39-45 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.
  7. Using jumper wires, apply battery voltage to VSV terminals. Air should flow from port "F". Remove jumper wires from VSV terminals. No air should pass through port "F". Replace VSV as necessary.
  8. If valve meets all specifications in steps 6) and 7), inspect circuits between EGR VSV and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
  9. Inspect EGR vacuum modulator. See SYSTEM & COMPONENT TESTING article. Replace as needed. If modulator is okay, inspect EGR valve. See SYSTEM & COMPONENT TESTING article. Replace EGR valve as necessary. If EGR valve is okay, go to next step.
  10. Disconnect EGR gas temperature sensor connector. Start engine. Ensure engine is at normal operating temperature. Run engine at 4000 RPM for 3 minutes and measure resistance between EGR gas temperature sensor terminals. If resistance is 4300 ohms or less, replace ECM and retest. If resistance is more than 4300 ohms, replace sensor.
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