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Home >> Toyota >> 1998 >> 4Runner Base, 4WD, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Tests W/Codes - 4-Cylinder >> Self-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. EGR temperature sensor is mounted near EGR valve. Using ohmmeter, measure resistance between EGR temperature 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 . 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. Measure voltage between terminals No. 9 (Brown/Black wire) and No. 11 (Pink 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 EGR valve vacuum hose. Replace vacuum hose as necessary. If vacuum hose is 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. 15 (Pink/Blue wire) at ECM E6 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 from port "F". Disconnect jumper wire. Air from port "E" should not flow from port "F". 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 EGR VSV terminals. Resistance should be 33-39 ohms at 68°F (20°C). Check for continuity between each terminal and body of EGR VSV. If continuity exists, replace EGR VSV. If continuity does not exist, 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 port "F". Remove battery voltage from EGR VSV terminals. Air from port "E" should not flow from port "F". Replace EGR VSV as necessary. If EGR VSV operates as specified, go to next step.
  8. Check for open circuit in wiring harness between engine compartment fuse block 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.
  10. Disconnect EGR 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 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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