LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Toyota >> 1995 >> T100 Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes - 2.7L >> Diagnostic Testing >> Code P0401 - Insufficient Exhaust Gas RECIRCULATION (EGR) Flow Detected >> Diagnosis & Repair (OBD-II Scan Tester ONLY)
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnosis & Repair (OBD-II Scan Tester ONLY)

  1. Disconnect EGR gas temperature sensor. Sensor is mounted in intake plenum. See Figure. Using ohmmeter, measure resistance between sensor terminals. If resistance is 600 k/ohms or less, go to next step. If resistance is NOT 600 k/ohms or less, inspect sensor. See the SYSTEM/COMPONENT TESTS - 2.7L article. Replace as needed.
  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. ECM is located behind glove box. Using DVOM, backprobe harness connector. Measure voltage between ECM terminals THG and E2. See Figure-7. If voltage is 4.5-5.5 volts, inspect circuits between EGR gas temperature sensor and ECM for open. See wiring diagram in the WIRING DIAGRAMS - 2.7L article. Repair as needed. If voltage is NOT 4.4-5.5 volts, replace ECM and retest.
  4. Inspect all EGR system vacuum hoses. Replace as needed. Check operation of EGR Vacuum Switching Valve (VSV). Access ECM. ECM is located behind glove box. Ensure ignition is off. Disconnect E7 harness connector. Turn ignition on. Using jumper wire, connect ECM terminal EGR to ground.
  5. VSV is located under intake plenum cover. With jumper wire connected, VSV is on. Air should flow through valve. Disconnect jumper wire. Air should NOT flow through valve. If valve operates correctly, go to step 9).
  6. If valve does operate correctly, 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. Replace VSV as needed.
  7. Check VSV operation. Apply battery voltage to valve terminals. Air should flow through valve. Remove battery voltage from valve terminals. Air should NOT flow through valve. Replace as needed.
  8. If valve meets all specifications in steps 6) and 7), inspect circuits between EGR VSV and ECM. See wiring diagram in the WIRING DIAGRAMS - 2.7L article. Repair as needed.
  9. Inspect EGR vacuum modulator. See procedures in the SYSTEM/COMPONENT TESTS - 2.7L article. Replace as needed. Inspect EGR valve. See the SYSTEM/COMPONENT TESTS article. Replace as needed.
  10. Check EGR gas temperature sensor resistance. Disconnect EGR gas temperature sensor connector. See Figure. Start and run engine. Disconnect EGR VSV harness connector. Run engine at 4000 RPM for 3 minutes. Measure resistance between sensor terminals. Resistance should be 4.3 k/ohms or less.
  11. If resistance is NOT within specification, replace sensor. If resistance is within specification, replace ECM and retest.
scientia non olet · About LEMON Manuals