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HOMESERVICE MANUALSTOYOTA1995T100 DX, RWD, STANDARDREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROLS - TESTS W/CODES - 2.7LDIAGNOSTIC TESTINGCODE P0401 - INSUFFICIENT EXHAUST GAS RECIRCULATION (EGR) FLOW DETECTEDDIAGNOSIS & REPAIR (TOYOTA SCAN TESTER ONLY)
1995 Toyota T100 DX, RWD, Standard

Diagnosis & Repair (Toyota Scan Tester ONLY)

1995 Toyota T100 DX, RWD, StandardSECTION Diagnosis & Repair (Toyota Scan Tester ONLY)
  1. Connect scan tester. See Figure. Turn ignition on. Read EGR gas temperature. Temperature should be 50°F (10°C). If temperature is within specification, go to step 6). If temperature is NOT within specification, go to next step. If temperature displayed is 37.6°F (3.1°C), there is an open EGR gas temperature sensor circuit.
  2. Disconnect EGR gas temperature sensor harness connector. Sensor is mounted in intake plenum. See Fig 1. Connect jumper wire between harness connector terminals.
  3. EGR gas temperature displayed should be 318.7°F (159.3°C). If temperature displayed is NOT within specification, go to next step. If temperature displayed is within specification, inspect sensor connectors and terminals. Repair as needed. If connectors are okay, replace sensor and retest.
  4. Remove jumper wire. Turn ignition off. Access ECM. ECM is located behind glove box. Connect jumper wire between ECM harness connector terminals THG and E2. See Figure-7. Turn ignition on. EGR gas temperature displayed should be 318.7°F (159.3°C).
  5. If temperature displayed is within specification, inspect and repair open in circuits between ECM and EGR gas temperature sensor. If temperature displayed is NOT within specification, replace ECM and retest.
  6. Inspect vacuum hoses. Repair as needed. If all hoses are okay, inspect VSV. On scan tester, select active test mode. Check operation of VSV when activated by scan tester. VSV is located under throttle body.
  7. Start and run engine. With system in OFF mode, air should flow through valve. With system in ON mode, air should NOT flow through valve. If valve operates correctly, go to step 11). If valve does NOT operate correctly, go to next step.
  8. 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.
  9. 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.
  10. If valve meets all specifications in steps 8) and 9), inspect circuits between EGR VSV and ECM. See wiring diagram in the WIRING DIAGRAMS - 2.7L article. Repair as needed.
  11. 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.
  12. Ensure all components are connected. Inspect EGR gas temperature sensor. Start and run engine. Select active test mode on scan tester (EGR system ON). Run engine at 4000 RPM for 3 minutes. Monitor EGR gas temperature. Temperature should be 284°F (140°C) or more.
  13. If temperature is NOT within specification, replace sensor. If temperature is within specification, replace ECM and retest.
Fig 1: EGR Temperature Sensor Harness Connector Location
G95H31408Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.