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Home >> Toyota >> 1998 >> T100 DX, 4WD, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Tests W/Codes - V6 >> Self-Diagnostic Tests >> DTC P0401: Insufficient Exhaust Gas RECIRCULATION (EGR) Flow Detected (2WD 1/2 Ton Models With Regular Cab) >> Diagnosis & Repair (Using OBD-II Scan Tool)
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Diagnosis & Repair (Using OBD-II Scan Tool)

  1. Disconnect EGR temperature sensor. EGR temperature sensor is mounted on EGR valve body on top right rear of engine. Using ohmmeter, measure resistance between sensor terminals. If resistance is 600,000 ohms or less, go to next step. If resistance is more than 600,000 ohms, check EGR temperature sensor. See appropriate SYSTEM/COMPONENT TESTS article. Replace EGR temperature sensor as necessary.
  2. Turn ignition on. Using DVOM, measure voltage between EGR temperature 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 passenger's side kick panel. Turn ignition on. Using DVOM, backprobe connector. Measure voltage between terminal No. 14 (Pink wire) at ECM E5 connector and terminal No. 22 (Brown/Black wire) at ECM E6 connector. See Figure. If voltage is 4.5-5.5 volts, check for open circuit in wiring harness between EGR temperature sensor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair wiring as necessary. If voltage is not 4.5-5.5 volts, replace ECM.
  4. Check all EGR system vacuum hoses. Replace vacuum hoses as necessary. If vacuum hoses are okay and routed properly, access ECM behind passenger's side kick panel. Ensure ignition is off. Disconnect ECM E5 connector. See Figure. Turn ignition on. Connect a jumper wire between ground and terminal No. 12 (Red/White wire) at ECM E5 connector.
  5. With jumper wire connected, EGR Vacuum Switching Valve (VSV) is on. Apply air pressure to EGR VSV port "E". See Figure. Air from port "E" should flow through filter on end of EGR VSV. Disconnect jumper wire. Air from port "E" should flow from port "G". If EGR VSV operates as specified, go to step 9). If EGR VSV does not operate as specified, go to next step.
  6. Turn ignition off. Remove EGR VSV. Using ohmmeter, measure resistance between VSV terminals. Resistance should be 33-39 ohms at 68°F (20°C). Measure resistance between each VSV terminal and body of EGR VSV. Resistance should be infinite. If resistance is not as specified, replace EGR VSV. If resistance is as specified, go to next step.
  7. Check EGR VSV operation. Apply battery voltage to VSV terminals. Apply air pressure to EGR VSV port "E". See Figure. Air from port "E" should flow from small filter on end of EGR VSV. Remove battery voltage from EGR VSV terminals. Air from port "E" should flow from port "G". Replace EGR VSV as necessary. If EGR VSV operates as specified, go to next step.
  8. Check for open circuit in wiring harness between EGR VSV and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair wiring as necessary.
  9. Check EGR vacuum modulator. See appropriate SYSTEM/COMPONENT TESTS article. Replace EGR vacuum modulator as necessary. If EGR vacuum modulator is okay, check EGR valve. See appropriate SYSTEM/COMPONENT TESTS article. Replace EGR valve 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. If resistance is more than 4300 ohms, replace EGR temperature sensor.
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