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Home >> Toyota >> 1996 >> T100 Base, 2D Pickup, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Tests W/Codes - 3.4L >> Circuit Tests >> DTC P0401 - Insufficient Exhaust Gas RECIRCULATION (EGR) Flow Detected (2WD Models) >> Diagnosis & Repair (Using OBD-II Scan Tester)
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Diagnosis & Repair (Using OBD-II Scan Tester)

  1. Disconnect EGR temperature sensor. Sensor is mounted on EGR valve body. 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 TESTS . Replace as necessary.
  2. Turn ignition on. Using DVOM, measure voltage between sensor wiring harness connector terminals. If voltage is 4.5-5.5 volts, go to step 4). If voltage is not 4.5-5.5 volts, go to next step.
  3. Access ECM behind glove box. Turn ignition on. Using DVOM, backprobe connector. On A/T models, measure voltage between terminal No. 21 (Pink wire) and No. 22 (Brown/Black wire) at ECM E6 connector. See Figure and Figure. On M/T models, measure voltage between terminals No. 9 (Brown/Black wire) and No. 14 (Pink wire) at ECM E6 connector. On all models, if voltage is 4.5-5.5 volts, check for an open circuit in wiring harness between EGR temperature sensor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If voltage is not 4.5-5.5 volts, replace ECM and retest.
  4. Inspect all EGR system vacuum hoses. Replace as necessary. Access ECM behind glove box. Ensure ignition is off. Disconnect ECM E5 connector (A/T models) or E7 connector (M/T models). Turn ignition on. On A/T models, connect a jumper wire between ground and terminal No. 8 (Red/White wire) at ECM E5 connector. On M/T models, connect a jumper wire between ground and terminal No. 18 (Red/White wire) at ECM E7 connector.
  5. With jumper wire connected, Vacuum Switching Valve (VSV) is on. Air from port "E" should exhaust through filter on end of valve. See Figure. Disconnect jumper wire. Air from port "E" should exhaust from port "G". If valve operates correctly, go to step 9). If valve does not operate correctly, go to next step.
  6. Turn ignition off. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 33-39 ohms at 68°F (20°C). Measure resistance between each terminal and body of valve. Resistance should be infinite. If resistance is not as specified, replace VSV. If resistance is as specified, go to next step.
  7. Check VSV operation. Apply battery voltage to VSV terminals. Air from port "E" should exhaust from small filter on end of valve. See Figure. Remove battery voltage from valve terminals. Air from port "E" should exhaust from port "G". Replace VSV as necessary. If VSV operates as specified, go to next step.
  8. Check for an open circuit in wiring harness between EGR VSV and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
  9. Inspect EGR vacuum modulator. See SYSTEM/COMPONENT TESTS article. Replace as necessary. If modulator is okay, inspect EGR valve. See SYSTEM/COMPONENT TESTS article. Replace as necessary. If components are okay, go to next step.
  10. Disconnect EGR temperature sensor connector. Start engine. Ensure engine is at normal operating temperature. Disconnect EGR VSV connector. Run engine at 4000 RPM for 3 minutes and measure resistance between EGR 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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